diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index c0bfcb7ade..cc31e5c657 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -802,6 +802,14 @@ nosave:
 	MOVL	AX, ret+16(FP)
 	RET
 
+#ifdef GOOS_windows
+// Dummy TLS that's used on Windows so that we don't crash trying
+// to restore the G register in needm. needm and its callees are
+// very careful never to actually use the G, the TLS just can't be
+// unset since we're in Go code.
+GLOBL zeroTLS<>(SB),RODATA,$const_tlsSize
+#endif
+
 // func cgocallback(fn, frame unsafe.Pointer, ctxt uintptr)
 // See cgocall.go for more details.
 TEXT ·cgocallback(SB),NOSPLIT,$24-24
@@ -825,6 +833,15 @@ TEXT ·cgocallback(SB),NOSPLIT,$24-24
 	MOVQ	BX, savedm-8(SP)	// saved copy of oldm
 	JMP	havem
 needm:
+#ifdef GOOS_windows
+	// Set up a dummy TLS value. needm is careful not to use it,
+	// but it needs to be there to prevent autogenerated code from
+	// crashing when it loads from it.
+	// We don't need to clear it or anything later because needm
+	// will set up TLS properly.
+	MOVQ	$zeroTLS<>(SB), DI
+	CALL	runtime·settls(SB)
+#endif
 	// On some platforms (Windows) we cannot call needm through
 	// an ABI wrapper because there's no TLS set up, and the ABI
 	// wrapper will try to restore the G register (R14) from TLS.
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index e5f948ec86..402d49ac82 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -482,17 +482,24 @@ type g struct {
 	gcAssistBytes int64
 }
 
+const (
+	// tlsSlots is the number of pointer-sized slots reserved for TLS on some platforms,
+	// like Windows.
+	tlsSlots = 6
+	tlsSize  = tlsSlots * sys.PtrSize
+)
+
 type m struct {
 	g0      *g     // goroutine with scheduling stack
 	morebuf gobuf  // gobuf arg to morestack
 	divmod  uint32 // div/mod denominator for arm - known to liblink
 
 	// Fields not known to debuggers.
-	procid        uint64       // for debuggers, but offset not hard-coded
-	gsignal       *g           // signal-handling g
-	goSigStack    gsignalStack // Go-allocated signal handling stack
-	sigmask       sigset       // storage for saved signal mask
-	tls           [6]uintptr   // thread-local storage (for x86 extern register)
+	procid        uint64            // for debuggers, but offset not hard-coded
+	gsignal       *g                // signal-handling g
+	goSigStack    gsignalStack      // Go-allocated signal handling stack
+	sigmask       sigset            // storage for saved signal mask
+	tls           [tlsSlots]uintptr // thread-local storage (for x86 extern register)
 	mstartfn      func()
 	curg          *g       // current running goroutine
 	caughtsig     guintptr // goroutine running during fatal signal