diff --git a/src/stage1/codegen.cpp b/src/stage1/codegen.cpp
index b8ac867082..825d05a31c 100644
--- a/src/stage1/codegen.cpp
+++ b/src/stage1/codegen.cpp
@@ -1433,6 +1433,9 @@ static void add_sentinel_check(CodeGen *g, LLVMValueRef sentinel_elem_ptr, ZigVa
 static LLVMValueRef gen_assert_zero(CodeGen *g, LLVMValueRef expr_val, ZigType *int_type) {
     LLVMValueRef zero = LLVMConstNull(get_llvm_type(g, int_type));
     LLVMValueRef ok_bit = LLVMBuildICmp(g->builder, LLVMIntEQ, expr_val, zero, "");
+    if (int_type->id == ZigTypeIdVector) {
+        ok_bit = ZigLLVMBuildAndReduce(g->builder, ok_bit);
+    }
     LLVMBasicBlockRef ok_block = LLVMAppendBasicBlock(g->cur_fn_val, "CastShortenOk");
     LLVMBasicBlockRef fail_block = LLVMAppendBasicBlock(g->cur_fn_val, "CastShortenFail");
     LLVMBuildCondBr(g->builder, ok_bit, ok_block, fail_block);
@@ -1450,29 +1453,37 @@ static LLVMValueRef gen_widen_or_shorten(CodeGen *g, bool want_runtime_safety, Z
     assert(actual_type->id == wanted_type->id);
     assert(expr_val != nullptr);
 
+    ZigType *scalar_actual_type = (actual_type->id == ZigTypeIdVector) ?
+        actual_type->data.vector.elem_type : actual_type;
+    ZigType *scalar_wanted_type = (wanted_type->id == ZigTypeIdVector) ?
+        wanted_type->data.vector.elem_type : wanted_type;
+
     uint64_t actual_bits;
     uint64_t wanted_bits;
-    if (actual_type->id == ZigTypeIdFloat) {
-        actual_bits = actual_type->data.floating.bit_count;
-        wanted_bits = wanted_type->data.floating.bit_count;
-    } else if (actual_type->id == ZigTypeIdInt) {
-        actual_bits = actual_type->data.integral.bit_count;
-        wanted_bits = wanted_type->data.integral.bit_count;
+    if (scalar_actual_type->id == ZigTypeIdFloat) {
+        actual_bits = scalar_actual_type->data.floating.bit_count;
+        wanted_bits = scalar_wanted_type->data.floating.bit_count;
+    } else if (scalar_actual_type->id == ZigTypeIdInt) {
+        actual_bits = scalar_actual_type->data.integral.bit_count;
+        wanted_bits = scalar_wanted_type->data.integral.bit_count;
     } else {
         zig_unreachable();
     }
 
-    if (actual_type->id == ZigTypeIdInt && want_runtime_safety && (
+    if (scalar_actual_type->id == ZigTypeIdInt && want_runtime_safety && (
         // negative to unsigned
-        (!wanted_type->data.integral.is_signed && actual_type->data.integral.is_signed) ||
+        (!scalar_wanted_type->data.integral.is_signed && scalar_actual_type->data.integral.is_signed) ||
         // unsigned would become negative
-        (wanted_type->data.integral.is_signed && !actual_type->data.integral.is_signed && actual_bits == wanted_bits)))
+        (scalar_wanted_type->data.integral.is_signed && !scalar_actual_type->data.integral.is_signed && actual_bits == wanted_bits)))
     {
         LLVMValueRef zero = LLVMConstNull(get_llvm_type(g, actual_type));
         LLVMValueRef ok_bit = LLVMBuildICmp(g->builder, LLVMIntSGE, expr_val, zero, "");
 
         LLVMBasicBlockRef ok_block = LLVMAppendBasicBlock(g->cur_fn_val, "SignCastOk");
         LLVMBasicBlockRef fail_block = LLVMAppendBasicBlock(g->cur_fn_val, "SignCastFail");
+        if (actual_type->id == ZigTypeIdVector) {
+            ok_bit = ZigLLVMBuildAndReduce(g->builder, ok_bit);
+        }
         LLVMBuildCondBr(g->builder, ok_bit, ok_block, fail_block);
 
         LLVMPositionBuilderAtEnd(g->builder, fail_block);
@@ -1484,10 +1495,10 @@ static LLVMValueRef gen_widen_or_shorten(CodeGen *g, bool want_runtime_safety, Z
     if (actual_bits == wanted_bits) {
         return expr_val;
     } else if (actual_bits < wanted_bits) {
-        if (actual_type->id == ZigTypeIdFloat) {
+        if (scalar_actual_type->id == ZigTypeIdFloat) {
             return LLVMBuildFPExt(g->builder, expr_val, get_llvm_type(g, wanted_type), "");
-        } else if (actual_type->id == ZigTypeIdInt) {
-            if (actual_type->data.integral.is_signed) {
+        } else if (scalar_actual_type->id == ZigTypeIdInt) {
+            if (scalar_actual_type->data.integral.is_signed) {
                 return LLVMBuildSExt(g->builder, expr_val, get_llvm_type(g, wanted_type), "");
             } else {
                 return LLVMBuildZExt(g->builder, expr_val, get_llvm_type(g, wanted_type), "");
@@ -1496,9 +1507,9 @@ static LLVMValueRef gen_widen_or_shorten(CodeGen *g, bool want_runtime_safety, Z
             zig_unreachable();
         }
     } else if (actual_bits > wanted_bits) {
-        if (actual_type->id == ZigTypeIdFloat) {
+        if (scalar_actual_type->id == ZigTypeIdFloat) {
             return LLVMBuildFPTrunc(g->builder, expr_val, get_llvm_type(g, wanted_type), "");
-        } else if (actual_type->id == ZigTypeIdInt) {
+        } else if (scalar_actual_type->id == ZigTypeIdInt) {
             if (wanted_bits == 0) {
                 if (!want_runtime_safety)
                     return nullptr;
@@ -1510,12 +1521,15 @@ static LLVMValueRef gen_widen_or_shorten(CodeGen *g, bool want_runtime_safety, Z
                 return trunc_val;
             }
             LLVMValueRef orig_val;
-            if (wanted_type->data.integral.is_signed) {
+            if (scalar_wanted_type->data.integral.is_signed) {
                 orig_val = LLVMBuildSExt(g->builder, trunc_val, get_llvm_type(g, actual_type), "");
             } else {
                 orig_val = LLVMBuildZExt(g->builder, trunc_val, get_llvm_type(g, actual_type), "");
             }
             LLVMValueRef ok_bit = LLVMBuildICmp(g->builder, LLVMIntEQ, expr_val, orig_val, "");
+            if (actual_type->id == ZigTypeIdVector) {
+                ok_bit = ZigLLVMBuildAndReduce(g->builder, ok_bit);
+            }
             LLVMBasicBlockRef ok_block = LLVMAppendBasicBlock(g->cur_fn_val, "CastShortenOk");
             LLVMBasicBlockRef fail_block = LLVMAppendBasicBlock(g->cur_fn_val, "CastShortenFail");
             LLVMBuildCondBr(g->builder, ok_bit, ok_block, fail_block);
diff --git a/src/stage1/ir.cpp b/src/stage1/ir.cpp
index ea9bf6ee8b..d638406a7b 100644
--- a/src/stage1/ir.cpp
+++ b/src/stage1/ir.cpp
@@ -86,6 +86,8 @@ enum ConstCastResultId {
     ConstCastResultIdCV,
     ConstCastResultIdPtrSentinel,
     ConstCastResultIdIntShorten,
+    ConstCastResultIdVectorLength,
+    ConstCastResultIdVectorChild,
 };
 
 struct ConstCastOnly;
@@ -914,6 +916,7 @@ static bool types_have_same_zig_comptime_repr(CodeGen *codegen, ZigType *expecte
     if (is_opt_err_set(expected) && is_opt_err_set(actual))
         return true;
 
+    // XXX: Vectors and arrays are interchangeable at comptime
     if (expected->id != actual->id)
         return false;
 
@@ -947,9 +950,11 @@ static bool types_have_same_zig_comptime_repr(CodeGen *codegen, ZigType *expecte
         case ZigTypeIdErrorUnion:
         case ZigTypeIdEnum:
         case ZigTypeIdUnion:
-        case ZigTypeIdVector:
         case ZigTypeIdFnFrame:
             return false;
+        case ZigTypeIdVector:
+            return expected->data.vector.len == actual->data.vector.len &&
+                    types_have_same_zig_comptime_repr(codegen, expected->data.vector.elem_type, actual->data.vector.elem_type);
         case ZigTypeIdArray:
             return expected->data.array.len == actual->data.array.len &&
                 expected->data.array.child_type == actual->data.array.child_type &&
@@ -12190,6 +12195,24 @@ static ConstCastOnly types_match_const_cast_only(IrAnalyze *ira, ZigType *wanted
         return result;
     }
 
+    if (wanted_type->id == ZigTypeIdVector && actual_type->id == ZigTypeIdVector) {
+        if (actual_type->data.vector.len != wanted_type->data.vector.len) {
+            result.id = ConstCastResultIdVectorLength;
+            return result;
+        }
+
+        ConstCastOnly child = types_match_const_cast_only(ira, wanted_type->data.vector.elem_type,
+                actual_type->data.vector.elem_type, source_node, false);
+        if (child.id == ConstCastResultIdInvalid)
+            return child;
+        if (child.id != ConstCastResultIdOk) {
+            result.id = ConstCastResultIdVectorChild;
+            return result;
+        }
+
+        return result;
+    }
+
     result.id = ConstCastResultIdType;
     result.data.type_mismatch = heap::c_allocator.allocate_nonzero<ConstCastTypeMismatch>(1);
     result.data.type_mismatch->wanted_type = wanted_type;
@@ -14306,37 +14329,62 @@ static IrInstGen *ir_analyze_enum_to_union(IrAnalyze *ira, IrInst* source_instr,
     return ira->codegen->invalid_inst_gen;
 }
 
+static bool value_numeric_fits_in_type(ZigValue *value, ZigType *type_entry);
+
 static IrInstGen *ir_analyze_widen_or_shorten(IrAnalyze *ira, IrInst* source_instr,
         IrInstGen *target, ZigType *wanted_type)
 {
-    assert(wanted_type->id == ZigTypeIdInt || wanted_type->id == ZigTypeIdFloat);
+    ZigType *wanted_scalar_type = (target->value->type->id == ZigTypeIdVector) ?
+        wanted_type->data.vector.elem_type : wanted_type;
+
+    assert(wanted_scalar_type->id == ZigTypeIdInt || wanted_scalar_type->id == ZigTypeIdFloat);
 
     if (instr_is_comptime(target)) {
         ZigValue *val = ir_resolve_const(ira, target, UndefBad);
         if (!val)
             return ira->codegen->invalid_inst_gen;
-        if (wanted_type->id == ZigTypeIdInt) {
-            if (bigint_cmp_zero(&val->data.x_bigint) == CmpLT && !wanted_type->data.integral.is_signed) {
+
+        if (wanted_scalar_type->id == ZigTypeIdInt) {
+            if (!wanted_scalar_type->data.integral.is_signed && value_cmp_numeric_val_any(val, CmpLT, nullptr)) {
                 ir_add_error(ira, source_instr,
                     buf_sprintf("attempt to cast negative value to unsigned integer"));
                 return ira->codegen->invalid_inst_gen;
             }
-            if (!bigint_fits_in_bits(&val->data.x_bigint, wanted_type->data.integral.bit_count,
-                    wanted_type->data.integral.is_signed))
-            {
+            if (!value_numeric_fits_in_type(val, wanted_scalar_type)) {
                 ir_add_error(ira, source_instr,
                     buf_sprintf("cast from '%s' to '%s' truncates bits",
-                        buf_ptr(&target->value->type->name), buf_ptr(&wanted_type->name)));
+                        buf_ptr(&target->value->type->name), buf_ptr(&wanted_scalar_type->name)));
                 return ira->codegen->invalid_inst_gen;
             }
         }
+
         IrInstGen *result = ir_const(ira, source_instr, wanted_type);
         result->value->type = wanted_type;
-        if (wanted_type->id == ZigTypeIdInt) {
-            bigint_init_bigint(&result->value->data.x_bigint, &val->data.x_bigint);
+
+        if (wanted_type->id == ZigTypeIdVector) {
+            result->value->data.x_array.data.s_none.elements = ira->codegen->pass1_arena->allocate<ZigValue>(wanted_type->data.vector.len);
+
+            for (size_t i = 0; i < wanted_type->data.vector.len; i++) {
+                ZigValue *scalar_dest_value = &result->value->data.x_array.data.s_none.elements[i];
+                ZigValue *scalar_src_value = &val->data.x_array.data.s_none.elements[i];
+
+                scalar_dest_value->type = wanted_scalar_type;
+                scalar_dest_value->special = ConstValSpecialStatic;
+
+                if (wanted_scalar_type->id == ZigTypeIdInt) {
+                    bigint_init_bigint(&scalar_dest_value->data.x_bigint, &scalar_src_value->data.x_bigint);
+                } else {
+                    float_init_float(scalar_dest_value, scalar_src_value);
+                }
+            }
         } else {
-            float_init_float(result->value, val);
+            if (wanted_type->id == ZigTypeIdInt) {
+                bigint_init_bigint(&result->value->data.x_bigint, &val->data.x_bigint);
+            } else {
+                float_init_float(result->value, val);
+            }
         }
+
         return result;
     }
 
@@ -14779,6 +14827,8 @@ static void report_recursive_error(IrAnalyze *ira, AstNode *source_node, ConstCa
                     actual_signed, actual_type->data.integral.bit_count));
             break;
         }
+        case ConstCastResultIdVectorLength: // TODO
+        case ConstCastResultIdVectorChild: // TODO
         case ConstCastResultIdFnAlign: // TODO
         case ConstCastResultIdFnVarArgs: // TODO
         case ConstCastResultIdFnReturnType: // TODO
@@ -15462,12 +15512,35 @@ static IrInstGen *ir_analyze_cast(IrAnalyze *ira, IrInst *source_instr,
     }
 
     // @Vector(N,T1) to @Vector(N,T2)
-    if (actual_type->id == ZigTypeIdVector && wanted_type->id == ZigTypeIdVector) {
-        if (actual_type->data.vector.len == wanted_type->data.vector.len &&
-            types_match_const_cast_only(ira, wanted_type->data.vector.elem_type,
-                actual_type->data.vector.elem_type, source_node, false).id == ConstCastResultIdOk)
+    if (actual_type->id == ZigTypeIdVector && wanted_type->id == ZigTypeIdVector &&
+            actual_type->data.vector.len == wanted_type->data.vector.len)
+    {
+        ZigType *scalar_actual_type = actual_type->data.vector.elem_type;
+        ZigType *scalar_wanted_type = wanted_type->data.vector.elem_type;
+
+        // widening conversion
+        if (scalar_wanted_type->id == ZigTypeIdInt &&
+            scalar_actual_type->id == ZigTypeIdInt &&
+            scalar_wanted_type->data.integral.is_signed == scalar_actual_type->data.integral.is_signed &&
+            scalar_wanted_type->data.integral.bit_count >= scalar_actual_type->data.integral.bit_count)
         {
-            return ir_analyze_bit_cast(ira, source_instr, value, wanted_type);
+            return ir_analyze_widen_or_shorten(ira, source_instr, value, wanted_type);
+        }
+
+        // small enough unsigned ints can get casted to large enough signed ints
+        if (scalar_wanted_type->id == ZigTypeIdInt && scalar_wanted_type->data.integral.is_signed &&
+            scalar_actual_type->id == ZigTypeIdInt && !scalar_actual_type->data.integral.is_signed &&
+            scalar_wanted_type->data.integral.bit_count > scalar_actual_type->data.integral.bit_count)
+        {
+            return ir_analyze_widen_or_shorten(ira, source_instr, value, wanted_type);
+        }
+
+        // float widening conversion
+        if (scalar_wanted_type->id == ZigTypeIdFloat &&
+            scalar_actual_type->id == ZigTypeIdFloat &&
+            scalar_wanted_type->data.floating.bit_count >= scalar_actual_type->data.floating.bit_count)
+        {
+            return ir_analyze_widen_or_shorten(ira, source_instr, value, wanted_type);
         }
     }
 
@@ -17728,6 +17801,33 @@ static bool is_pointer_arithmetic_allowed(ZigType *lhs_type, IrBinOp op) {
     zig_unreachable();
 }
 
+// Returns true if integer `value` can be converted to `type_entry` without
+// losing data.
+// If `value` is a vector the function returns true if this is valid for every
+// element.
+static bool value_numeric_fits_in_type(ZigValue *value, ZigType *type_entry) {
+    assert(value->special == ConstValSpecialStatic);
+    assert(type_entry->id == ZigTypeIdInt);
+
+    switch (value->type->id) {
+        case ZigTypeIdComptimeInt:
+        case ZigTypeIdInt: {
+            return bigint_fits_in_bits(&value->data.x_bigint, type_entry->data.integral.bit_count,
+                    type_entry->data.integral.is_signed);
+        }
+        case ZigTypeIdVector: {
+            for (size_t i = 0; i < value->type->data.vector.len; i++) {
+                ZigValue *scalar_value = &value->data.x_array.data.s_none.elements[i];
+                const bool result = bigint_fits_in_bits(&scalar_value->data.x_bigint,
+                        type_entry->data.integral.bit_count, type_entry->data.integral.is_signed);
+                if (!result) return false;
+            }
+            return true;
+        }
+        default: zig_unreachable();
+    }
+}
+
 static bool value_cmp_numeric_val(ZigValue *left, Cmp predicate, ZigValue *right, bool any) {
     assert(left->special == ConstValSpecialStatic);
     assert(right == nullptr || right->special == ConstValSpecialStatic);
@@ -27154,8 +27254,12 @@ static IrInstGen *ir_analyze_instruction_int_cast(IrAnalyze *ira, IrInstSrcIntCa
     if (type_is_invalid(dest_type))
         return ira->codegen->invalid_inst_gen;
 
-    if (dest_type->id != ZigTypeIdInt && dest_type->id != ZigTypeIdComptimeInt) {
-        ir_add_error(ira, &instruction->dest_type->base, buf_sprintf("expected integer type, found '%s'", buf_ptr(&dest_type->name)));
+    ZigType *scalar_dest_type = (dest_type->id == ZigTypeIdVector) ?
+        dest_type->data.vector.elem_type : dest_type;
+
+    if (scalar_dest_type->id != ZigTypeIdInt && scalar_dest_type->id != ZigTypeIdComptimeInt) {
+        ir_add_error(ira, &instruction->dest_type->base,
+                buf_sprintf("expected integer type, found '%s'", buf_ptr(&scalar_dest_type->name)));
         return ira->codegen->invalid_inst_gen;
     }
 
@@ -27163,13 +27267,16 @@ static IrInstGen *ir_analyze_instruction_int_cast(IrAnalyze *ira, IrInstSrcIntCa
     if (type_is_invalid(target->value->type))
         return ira->codegen->invalid_inst_gen;
 
-    if (target->value->type->id != ZigTypeIdInt && target->value->type->id != ZigTypeIdComptimeInt) {
+    ZigType *scalar_target_type = (target->value->type->id == ZigTypeIdVector) ?
+        target->value->type->data.vector.elem_type : target->value->type;
+
+    if (scalar_target_type->id != ZigTypeIdInt && scalar_target_type->id != ZigTypeIdComptimeInt) {
         ir_add_error(ira, &instruction->target->base, buf_sprintf("expected integer type, found '%s'",
-                    buf_ptr(&target->value->type->name)));
+                    buf_ptr(&scalar_target_type->name)));
         return ira->codegen->invalid_inst_gen;
     }
 
-    if (instr_is_comptime(target) || dest_type->id == ZigTypeIdComptimeInt) {
+    if (scalar_dest_type->id == ZigTypeIdComptimeInt) {
         ZigValue *val = ir_resolve_const(ira, target, UndefBad);
         if (val == nullptr)
             return ira->codegen->invalid_inst_gen;
@@ -27222,6 +27329,7 @@ static IrInstGen *ir_analyze_instruction_float_cast(IrAnalyze *ira, IrInstSrcFlo
         if (val == nullptr)
             return ira->codegen->invalid_inst_gen;
 
+        // XXX: This will trigger an assertion failure if dest_type is comptime_float
         return ir_analyze_widen_or_shorten(ira, &instruction->target->base, target, dest_type);
     }
 
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index 062a357a93..1d3a2a6ea1 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -2944,7 +2944,6 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         "tmp.zig:4:18: error: expected type 'fn(i32) void', found 'fn(bool) void",
         "tmp.zig:4:18: note: parameter 0: 'bool' cannot cast into 'i32'",
     });
-
     cases.add("cast negative value to unsigned integer",
         \\comptime {
         \\    const value: i32 = -1;
@@ -2955,7 +2954,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\    const unsigned: u32 = value;
         \\}
     , &[_][]const u8{
-        "tmp.zig:3:36: error: cannot cast negative value -1 to unsigned integer type 'u32'",
+        "tmp.zig:3:22: error: attempt to cast negative value to unsigned integer",
         "tmp.zig:7:27: error: cannot cast negative value -1 to unsigned integer type 'u32'",
     });
 
@@ -2977,7 +2976,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\    var unsigned: u64 = signed;
         \\}
     , &[_][]const u8{
-        "tmp.zig:3:31: error: integer value 300 cannot be coerced to type 'u8'",
+        "tmp.zig:3:18: error: cast from 'u16' to 'u8' truncates bits",
         "tmp.zig:7:22: error: integer value 300 cannot be coerced to type 'u8'",
         "tmp.zig:11:20: error: expected type 'u8', found 'u16'",
         "tmp.zig:11:20: note: unsigned 8-bit int cannot represent all possible unsigned 16-bit values",
diff --git a/test/runtime_safety.zig b/test/runtime_safety.zig
index 8d962b088e..a0b4a555a5 100644
--- a/test/runtime_safety.zig
+++ b/test/runtime_safety.zig
@@ -70,6 +70,36 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         );
     }
 
+    cases.addRuntimeSafety("truncating vector cast",
+        \\const std = @import("std");
+        \\const V = @import("std").meta.Vector;
+        \\pub fn panic(message: []const u8, stack_trace: ?*@import("builtin").StackTrace) noreturn {
+        \\    if (std.mem.eql(u8, message, "integer cast truncated bits")) {
+        \\        std.process.exit(126); // good
+        \\    }
+        \\    std.process.exit(0); // test failed
+        \\}
+        \\pub fn main() void {
+        \\    var x = @splat(4, @as(u32, 0xdeadbeef));
+        \\    var y = @intCast(V(4, u16), x);
+        \\}
+    );
+
+    cases.addRuntimeSafety("unsigned-signed vector cast",
+        \\const std = @import("std");
+        \\const V = @import("std").meta.Vector;
+        \\pub fn panic(message: []const u8, stack_trace: ?*@import("builtin").StackTrace) noreturn {
+        \\    if (std.mem.eql(u8, message, "attempt to cast negative value to unsigned integer")) {
+        \\        std.process.exit(126); // good
+        \\    }
+        \\    std.process.exit(0); // test failed
+        \\}
+        \\pub fn main() void {
+        \\    var x = @splat(4, @as(u32, 0x80000000));
+        \\    var y = @intCast(V(4, i32), x);
+        \\}
+    );
+
     cases.addRuntimeSafety("shift left by huge amount",
         \\const std = @import("std");
         \\pub fn panic(message: []const u8, stack_trace: ?*@import("builtin").StackTrace) noreturn {
diff --git a/test/stage1/behavior/cast.zig b/test/stage1/behavior/cast.zig
index 0eb00512b9..d39b20a7e1 100644
--- a/test/stage1/behavior/cast.zig
+++ b/test/stage1/behavior/cast.zig
@@ -2,6 +2,7 @@ const std = @import("std");
 const expect = std.testing.expect;
 const mem = std.mem;
 const maxInt = std.math.maxInt;
+const Vector = std.meta.Vector;
 
 test "int to ptr cast" {
     const x = @as(usize, 13);
@@ -364,6 +365,43 @@ test "@floatCast comptime_int and comptime_float" {
     }
 }
 
+test "vector casts" {
+    const S = struct {
+        fn doTheTest() void {
+            // Upcast (implicit, equivalent to @intCast)
+            var up0: Vector(2, u8) = [_]u8{ 0x55, 0xaa };
+            var up1 = @as(Vector(2, u16), up0);
+            var up2 = @as(Vector(2, u32), up0);
+            var up3 = @as(Vector(2, u64), up0);
+            // Downcast (safety-checked)
+            var down0 = up3;
+            var down1 = @intCast(Vector(2, u32), down0);
+            var down2 = @intCast(Vector(2, u16), down0);
+            var down3 = @intCast(Vector(2, u8), down0);
+
+            expect(mem.eql(u16, &@as([2]u16, up1), &[2]u16{ 0x55, 0xaa }));
+            expect(mem.eql(u32, &@as([2]u32, up2), &[2]u32{ 0x55, 0xaa }));
+            expect(mem.eql(u64, &@as([2]u64, up3), &[2]u64{ 0x55, 0xaa }));
+
+            expect(mem.eql(u32, &@as([2]u32, down1), &[2]u32{ 0x55, 0xaa }));
+            expect(mem.eql(u16, &@as([2]u16, down2), &[2]u16{ 0x55, 0xaa }));
+            expect(mem.eql(u8, &@as([2]u8, down3), &[2]u8{ 0x55, 0xaa }));
+        }
+
+        fn doTheTestFloat() void {
+            var vec = @splat(2, @as(f32, 1234.0));
+            var wider: Vector(2, f64) = vec;
+            expect(wider[0] == 1234.0);
+            expect(wider[1] == 1234.0);
+        }
+    };
+
+    S.doTheTest();
+    comptime S.doTheTest();
+    S.doTheTestFloat();
+    comptime S.doTheTestFloat();
+}
+
 test "comptime_int @intToFloat" {
     {
         const result = @intToFloat(f16, 1234);