diff --git a/src/pkg/runtime/darwin/mem.c b/src/pkg/runtime/darwin/mem.c
index f6fbe5016d..32bedd0950 100644
--- a/src/pkg/runtime/darwin/mem.c
+++ b/src/pkg/runtime/darwin/mem.c
@@ -21,6 +21,7 @@ SysUnused(void *v, uintptr n)
 void
 SysFree(void *v, uintptr n)
 {
+	mstats.sys -= n;
 	runtime_munmap(v, n);
 }
 
diff --git a/src/pkg/runtime/freebsd/mem.c b/src/pkg/runtime/freebsd/mem.c
index f6fbe5016d..32bedd0950 100644
--- a/src/pkg/runtime/freebsd/mem.c
+++ b/src/pkg/runtime/freebsd/mem.c
@@ -21,6 +21,7 @@ SysUnused(void *v, uintptr n)
 void
 SysFree(void *v, uintptr n)
 {
+	mstats.sys -= n;
 	runtime_munmap(v, n);
 }
 
diff --git a/src/pkg/runtime/linux/mem.c b/src/pkg/runtime/linux/mem.c
index ab47787f6c..bad67001c4 100644
--- a/src/pkg/runtime/linux/mem.c
+++ b/src/pkg/runtime/linux/mem.c
@@ -33,6 +33,7 @@ SysUnused(void *v, uintptr n)
 void
 SysFree(void *v, uintptr n)
 {
+	mstats.sys -= n;
 	runtime_munmap(v, n);
 }
 
diff --git a/src/pkg/runtime/nacl/mem.c b/src/pkg/runtime/nacl/mem.c
index 0bdd38211e..057ae04e52 100644
--- a/src/pkg/runtime/nacl/mem.c
+++ b/src/pkg/runtime/nacl/mem.c
@@ -26,6 +26,7 @@ void
 SysFree(void *v, uintptr n)
 {
 	// round to page size or else nacl prints annoying log messages
+	mstats.sys -= n;
 	n = (n+NaclPage-1) & ~(NaclPage-1);
 	runtime_munmap(v, n);
 }