diff --git a/core/c/c.odin b/core/c/c.odin
index 8266bf38a..bc847d566 100644
--- a/core/c/c.odin
+++ b/core/c/c.odin
@@ -49,7 +49,7 @@ int_least64_t  :: builtin.i64
 uint_least64_t :: builtin.u64
 
 // Same on Windows, Linux, and FreeBSD
-when ODIN_ARCH == .i386 || ODIN_ARCH == .amd64 {
+when ODIN_ARCH == .i386 {
 	int_fast8_t    :: builtin.i8
 	uint_fast8_t   :: builtin.u8
 	int_fast16_t   :: builtin.i32
@@ -58,6 +58,15 @@ when ODIN_ARCH == .i386 || ODIN_ARCH == .amd64 {
 	uint_fast32_t  :: builtin.u32
 	int_fast64_t   :: builtin.i64
 	uint_fast64_t  :: builtin.u64
+} else when ODIN_ARCH == .amd64 {
+	int_fast8_t    :: builtin.i8
+	uint_fast8_t   :: builtin.u8
+	int_fast16_t   :: long
+	uint_fast16_t  :: ulong
+	int_fast32_t   :: long
+	uint_fast32_t  :: ulong
+	int_fast64_t   :: builtin.i64
+	uint_fast64_t  :: builtin.u64
 } else {
 	int_fast8_t    :: builtin.i8
 	uint_fast8_t   :: builtin.u8