diff --git a/src/runtime/sys_linux_amd64.s b/src/runtime/sys_linux_amd64.s
index aed85cb0aa0..f407078176a 100644
--- a/src/runtime/sys_linux_amd64.s
+++ b/src/runtime/sys_linux_amd64.s
@@ -258,7 +258,7 @@ TEXT runtime·sysMmap(SB),NOSPLIT,$0
 
 // Call the function stored in _cgo_mmap using the GCC calling convention.
 // This must be called on the system stack.
-TEXT runtime·callCgoMmap(SB),NOSPLIT,$0
+TEXT runtime·callCgoMmap(SB),NOSPLIT,$16
 	MOVQ	addr+0(FP), DI
 	MOVQ	n+8(FP), SI
 	MOVL	prot+16(FP), DX
@@ -266,7 +266,11 @@ TEXT runtime·callCgoMmap(SB),NOSPLIT,$0
 	MOVL	fd+24(FP), R8
 	MOVL	off+28(FP), R9
 	MOVQ	_cgo_mmap(SB), AX
+	MOVQ	SP, BX
+	ANDQ	$~15, SP	// alignment as per amd64 psABI
+	MOVQ	BX, 0(SP)
 	CALL	AX
+	MOVQ	0(SP), SP
 	MOVQ	AX, ret+32(FP)
 	RET