diff --git a/src/pkg/runtime/darwin/amd64/sys.s b/src/pkg/runtime/darwin/amd64/sys.s
index 6d3460ff06..0b85d27db7 100644
--- a/src/pkg/runtime/darwin/amd64/sys.s
+++ b/src/pkg/runtime/darwin/amd64/sys.s
@@ -77,11 +77,11 @@ TEXT sigtramp(SB),7,$40
 
 TEXT	·mmap(SB),7,$0
 	MOVQ	8(SP), DI		// arg 1 addr
-	MOVL	16(SP), SI		// arg 2 len
-	MOVL	20(SP), DX		// arg 3 prot
-	MOVL	24(SP), R10		// arg 4 flags
-	MOVL	28(SP), R8		// arg 5 fid
-	MOVL	32(SP), R9		// arg 6 offset
+	MOVQ	16(SP), SI		// arg 2 len
+	MOVL	24(SP), DX		// arg 3 prot
+	MOVL	28(SP), R10		// arg 4 flags
+	MOVL	32(SP), R8		// arg 5 fid
+	MOVL	36(SP), R9		// arg 6 offset
 	MOVL	$(0x2000000+197), AX	// syscall entry
 	SYSCALL
 	JCC	2(PC)
diff --git a/src/pkg/runtime/freebsd/amd64/sys.s b/src/pkg/runtime/freebsd/amd64/sys.s
index 506db29f8e..604b763ab9 100644
--- a/src/pkg/runtime/freebsd/amd64/sys.s
+++ b/src/pkg/runtime/freebsd/amd64/sys.s
@@ -91,13 +91,13 @@ TEXT	sigtramp(SB),7,$24-16
 	CALL	sighandler(SB)
 	RET
 
-TEXT	·mmap(SB),7,$-8
+TEXT	·mmap(SB),7,$0
 	MOVQ	8(SP), DI		// arg 1 addr
-	MOVL	16(SP), SI		// arg 2 len
-	MOVL	20(SP), DX		// arg 3 prot
-	MOVL	24(SP), R10		// arg 4 flags
-	MOVL	28(SP), R8		// arg 5 fid
-	MOVL	32(SP), R9		// arg 6 offset
+	MOVQ	16(SP), SI		// arg 2 len
+	MOVL	24(SP), DX		// arg 3 prot
+	MOVL	28(SP), R10		// arg 4 flags
+	MOVL	32(SP), R8		// arg 5 fid
+	MOVL	36(SP), R9		// arg 6 offset
 	MOVL	$477, AX
 	SYSCALL
 	JCC	2(PC)
diff --git a/src/pkg/runtime/linux/amd64/sys.s b/src/pkg/runtime/linux/amd64/sys.s
index 882ccf1d26..dd04731581 100644
--- a/src/pkg/runtime/linux/amd64/sys.s
+++ b/src/pkg/runtime/linux/amd64/sys.s
@@ -76,14 +76,14 @@ TEXT	sigreturn(SB),7,$0
 	SYSCALL
 	INT $3	// not reached
 
-TEXT	·mmap(SB),7,$0-32
+TEXT	·mmap(SB),7,$0
 	MOVQ	8(SP), DI
 	MOVQ	$0, SI
-	MOVL	16(SP), SI
-	MOVL	20(SP), DX
-	MOVL	24(SP), R10
-	MOVL	28(SP), R8
-	MOVL	32(SP), R9
+	MOVQ	16(SP), SI
+	MOVL	24(SP), DX
+	MOVL	28(SP), R10
+	MOVL	32(SP), R8
+	MOVL	36(SP), R9
 
 	MOVL	$9, AX			// syscall entry
 	SYSCALL
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index 0b770ad0e1..e2aedb4cee 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -511,7 +511,7 @@ void	notewakeup(Note*);
 /*
  * low level go-called
  */
-uint8*	runtime_mmap(byte*, uint32, int32, int32, int32, uint32);
+uint8*	runtime_mmap(byte*, uintptr, int32, int32, int32, uint32);
 void	runtime_memclr(byte*, uint32);
 void	runtime_setcallerpc(void*, void*);
 void*	runtime_getcallerpc(void*);