diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index e0803866c80..8ead173e64d 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -57,18 +57,19 @@ func (p *Package) writeDefs() {
 	fflg.Close()
 
 	// Write C main file for using gcc to resolve imports.
+	fmt.Fprintf(fm, "#include <stddef.h>\n") // For size_t below.
 	fmt.Fprintf(fm, "int main() { return 0; }\n")
 	if *importRuntimeCgo {
-		fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*) __attribute__((unused)), void *a __attribute__((unused)), int c __attribute__((unused)), __SIZE_TYPE__ ctxt __attribute__((unused))) { }\n")
-		fmt.Fprintf(fm, "__SIZE_TYPE__ _cgo_wait_runtime_init_done(void) { return 0; }\n")
-		fmt.Fprintf(fm, "void _cgo_release_context(__SIZE_TYPE__ ctxt __attribute__((unused))) { }\n")
+		fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*) __attribute__((unused)), void *a __attribute__((unused)), int c __attribute__((unused)), size_t ctxt __attribute__((unused))) { }\n")
+		fmt.Fprintf(fm, "size_t _cgo_wait_runtime_init_done(void) { return 0; }\n")
+		fmt.Fprintf(fm, "void _cgo_release_context(size_t ctxt __attribute__((unused))) { }\n")
 		fmt.Fprintf(fm, "char* _cgo_topofstack(void) { return (char*)0; }\n")
 	} else {
 		// If we're not importing runtime/cgo, we *are* runtime/cgo,
 		// which provides these functions. We just need a prototype.
-		fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*), void *a, int c, __SIZE_TYPE__ ctxt);\n")
-		fmt.Fprintf(fm, "__SIZE_TYPE__ _cgo_wait_runtime_init_done(void);\n")
-		fmt.Fprintf(fm, "void _cgo_release_context(__SIZE_TYPE__);\n")
+		fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*), void *a, int c, size_t ctxt);\n")
+		fmt.Fprintf(fm, "size_t _cgo_wait_runtime_init_done(void);\n")
+		fmt.Fprintf(fm, "void _cgo_release_context(size_t);\n")
 	}
 	fmt.Fprintf(fm, "void _cgo_allocate(void *a __attribute__((unused)), int c __attribute__((unused))) { }\n")
 	fmt.Fprintf(fm, "void _cgo_panic(void *a __attribute__((unused)), int c __attribute__((unused))) { }\n")
@@ -886,9 +887,9 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 	fmt.Fprintf(fgcc, "#pragma GCC diagnostic ignored \"-Wpragmas\"\n")
 	fmt.Fprintf(fgcc, "#pragma GCC diagnostic ignored \"-Waddress-of-packed-member\"\n")
 
-	fmt.Fprintf(fgcc, "extern void crosscall2(void (*fn)(void *), void *, int, __SIZE_TYPE__);\n")
-	fmt.Fprintf(fgcc, "extern __SIZE_TYPE__ _cgo_wait_runtime_init_done(void);\n")
-	fmt.Fprintf(fgcc, "extern void _cgo_release_context(__SIZE_TYPE__);\n\n")
+	fmt.Fprintf(fgcc, "extern void crosscall2(void (*fn)(void *), void *, int, size_t);\n")
+	fmt.Fprintf(fgcc, "extern size_t _cgo_wait_runtime_init_done(void);\n")
+	fmt.Fprintf(fgcc, "extern void _cgo_release_context(size_t);\n\n")
 	fmt.Fprintf(fgcc, "extern char* _cgo_topofstack(void);")
 	fmt.Fprintf(fgcc, "%s\n", tsanProlog)
 	fmt.Fprintf(fgcc, "%s\n", msanProlog)
@@ -992,7 +993,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		fmt.Fprintf(fgcc, "\nCGO_NO_SANITIZE_THREAD")
 		fmt.Fprintf(fgcc, "\n%s\n", s)
 		fmt.Fprintf(fgcc, "{\n")
-		fmt.Fprintf(fgcc, "\t__SIZE_TYPE__ _cgo_ctxt = _cgo_wait_runtime_init_done();\n")
+		fmt.Fprintf(fgcc, "\tsize_t _cgo_ctxt = _cgo_wait_runtime_init_done();\n")
 		// The results part of the argument structure must be
 		// initialized to 0 so the write barriers generated by
 		// the assignments to these fields in Go are safe.
@@ -1561,7 +1562,7 @@ var msanProlog = noMsanProlog
 
 const builtinProlog = `
 #line 1 "cgo-builtin-prolog"
-#include <stddef.h> /* for ptrdiff_t and size_t below */
+#include <stddef.h>
 
 /* Define intgo when compiling with GCC.  */
 typedef ptrdiff_t intgo;
@@ -1845,7 +1846,7 @@ void localCgoCheckResult(Eface val) {
 const builtinExportProlog = `
 #line 1 "cgo-builtin-export-prolog"
 
-#include <stddef.h> /* for ptrdiff_t below */
+#include <stddef.h>
 
 #ifndef GO_CGO_EXPORT_PROLOGUE_H
 #define GO_CGO_EXPORT_PROLOGUE_H
@@ -1891,7 +1892,7 @@ typedef long long GoInt64;
 typedef unsigned long long GoUint64;
 typedef GoIntGOINTBITS GoInt;
 typedef GoUintGOINTBITS GoUint;
-typedef __SIZE_TYPE__ GoUintptr;
+typedef size_t GoUintptr;
 typedef float GoFloat32;
 typedef double GoFloat64;
 typedef float _Complex GoComplex64;
@@ -1941,5 +1942,5 @@ static void GoInit(void) {
 		runtime_iscgo = 1;
 }
 
-extern __SIZE_TYPE__ _cgo_wait_runtime_init_done(void) __attribute__ ((weak));
+extern size_t _cgo_wait_runtime_init_done(void) __attribute__ ((weak));
 `