diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index b0c918bc21fa..24c9d40435d7 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -154,6 +154,10 @@ SYSINIT(cpu, SI_SUB_CPU, SI_ORDER_FIRST, cpu_startup, NULL)
 extern vm_offset_t ksym_start, ksym_end;
 #endif
 
+/* Intel ICH registers */
+#define ICH_PMBASE	0x400
+#define ICH_SMI_EN	ICH_PMBASE + 0x30
+
 int	_udatasel, _ucodesel, _ucode32sel;
 
 int cold = 1;
@@ -185,6 +189,27 @@ static void
 cpu_startup(dummy)
 	void *dummy;
 {
+	char *sysenv;
+
+	/*
+	 * On MacBooks, we need to disallow the legacy USB circuit to
+	 * generate an SMI# because this can cause several problems,
+	 * namely: incorrect CPU frequency detection and failure to
+	 * start the APs.
+	 * We do this by disabling a bit in the SMI_EN (SMI Control and
+	 * Enable register) of the Intel ICH LPC Interface Bridge. 
+	 */
+	sysenv = getenv("smbios.system.product");
+	if (sysenv != NULL) {
+		if (strncmp(sysenv, "MacBook", 7) == 0) {
+			if (bootverbose)
+				printf("Disabling LEGACY_USB_EN bit on "
+				    "Intel ICH.\n");
+			outl(ICH_SMI_EN, inl(ICH_SMI_EN) & ~0x8);
+		}
+		freeenv(sysenv);
+	}
+
 	/*
 	 * Good {morning,afternoon,evening,night}.
 	 */