diff --git a/src/runtime/cgo/gcc_mmap.c b/src/runtime/cgo/gcc_mmap.c
index 698a7e3cd2..83d857f0d1 100644
--- a/src/runtime/cgo/gcc_mmap.c
+++ b/src/runtime/cgo/gcc_mmap.c
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,amd64 linux,arm64 linux,ppc64le
+// +build linux,amd64 linux,arm64 linux,ppc64le freebsd,amd64
 
 #include <errno.h>
 #include <stdint.h>
diff --git a/src/runtime/cgo/mmap.go b/src/runtime/cgo/mmap.go
index eae0a9e7cc..2f7e83bcb7 100644
--- a/src/runtime/cgo/mmap.go
+++ b/src/runtime/cgo/mmap.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (linux && amd64) || (linux && arm64)
+//go:build (linux && amd64) || (linux && arm64) || (freebsd && amd64)
 
 package cgo
 
diff --git a/src/runtime/cgo_mmap.go b/src/runtime/cgo_mmap.go
index 4cb3e65f14..30660f7784 100644
--- a/src/runtime/cgo_mmap.go
+++ b/src/runtime/cgo_mmap.go
@@ -4,7 +4,7 @@
 
 // Support for memory sanitizer. See runtime/cgo/mmap.go.
 
-//go:build (linux && amd64) || (linux && arm64)
+//go:build (linux && amd64) || (linux && arm64) || (freebsd && amd64)
 
 package runtime
 
diff --git a/src/runtime/mmap.go b/src/runtime/mmap.go
index 3280a62e8d..f0183f61cf 100644
--- a/src/runtime/mmap.go
+++ b/src/runtime/mmap.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !aix && !darwin && !js && (!linux || !amd64) && (!linux || !arm64) && !openbsd && !plan9 && !solaris && !windows
+//go:build !aix && !darwin && !js && (!linux || !amd64) && (!linux || !arm64) && (!freebsd || !amd64) && !openbsd && !plan9 && !solaris && !windows
 
 package runtime
 
diff --git a/src/runtime/msan/msan.go b/src/runtime/msan/msan.go
index f1bf4e1065..4e41f8528d 100644
--- a/src/runtime/msan/msan.go
+++ b/src/runtime/msan/msan.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build msan && linux && (amd64 || arm64)
+//go:build msan && ((linux && (amd64 || arm64)) || (freebsd && amd64))
 
 package msan
 
diff --git a/src/runtime/sys_freebsd_amd64.s b/src/runtime/sys_freebsd_amd64.s
index 35311398da..c266d73ea2 100644
--- a/src/runtime/sys_freebsd_amd64.s
+++ b/src/runtime/sys_freebsd_amd64.s
@@ -385,7 +385,7 @@ sigtrampnog:
 	MOVQ	_cgo_callers(SB), AX
 	JMP	AX
 
-TEXT runtime·mmap(SB),NOSPLIT,$0
+TEXT runtime·sysMmap(SB),NOSPLIT,$0
 	MOVQ	addr+0(FP), DI		// arg 1 addr
 	MOVQ	n+8(FP), SI		// arg 2 len
 	MOVL	prot+16(FP), DX		// arg 3 prot
@@ -403,7 +403,25 @@ ok:
 	MOVQ	$0, err+40(FP)
 	RET
 
-TEXT runtime·munmap(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,$16
+	MOVQ	addr+0(FP), DI
+	MOVQ	n+8(FP), SI
+	MOVL	prot+16(FP), DX
+	MOVL	flags+20(FP), CX
+	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
+
+TEXT runtime·sysMunmap(SB),NOSPLIT,$0
 	MOVQ	addr+0(FP), DI		// arg 1 addr
 	MOVQ	n+8(FP), SI		// arg 2 len
 	MOVL	$SYS_munmap, AX
@@ -412,6 +430,19 @@ TEXT runtime·munmap(SB),NOSPLIT,$0
 	MOVL	$0xf1, 0xf1  // crash
 	RET
 
+// Call the function stored in _cgo_munmap using the GCC calling convention.
+// This must be called on the system stack.
+TEXT runtime·callCgoMunmap(SB),NOSPLIT,$16-16
+	MOVQ	addr+0(FP), DI
+	MOVQ	n+8(FP), SI
+	MOVQ	_cgo_munmap(SB), AX
+	MOVQ	SP, BX
+	ANDQ	$~15, SP	// alignment as per amd64 psABI
+	MOVQ	BX, 0(SP)
+	CALL	AX
+	MOVQ	0(SP), SP
+	RET
+
 TEXT runtime·madvise(SB),NOSPLIT,$0
 	MOVQ	addr+0(FP), DI
 	MOVQ	n+8(FP), SI