diff --git a/reactos/include/crt/mingw32/intrin_x86.h b/reactos/include/crt/mingw32/intrin_x86.h
index 7ac21642230..0824c6dd341 100644
--- a/reactos/include/crt/mingw32/intrin_x86.h
+++ b/reactos/include/crt/mingw32/intrin_x86.h
@@ -974,6 +974,23 @@ static __inline__ __attribute__((always_inline)) unsigned long long __emulu(cons
 	return retval;
 }
 
+#ifdef _M_AMD64
+
+static __inline__ __attribute__((always_inline)) __int64 __mulh(__int64 a, __int64 b)
+{
+	__int64 retval;
+	__asm__("imulq %[b]" : "=d" (retval) : [a] "a" (a), [b] "rm" (b));
+	return retval;
+}
+
+static __inline__ __attribute__((always_inline)) unsigned __int64 __umulh(unsigned __int64 a, unsigned __int64 b)
+{
+	unsigned __int64 retval;
+	__asm__("mulq %[b]" : "=d" (retval) : [a] "a" (a), [b] "rm" (b));
+	return retval;
+}
+
+#endif
 
 /*** Port I/O ***/
 static __inline__ __attribute__((always_inline)) unsigned char __inbyte(const unsigned short Port)