diff --git a/diff.go b/diff.go
index 014cff5..b8f3780 100644
--- a/diff.go
+++ b/diff.go
@@ -147,6 +147,7 @@ func (diff *Diff) Free() error {
 	}
 	runtime.SetFinalizer(diff, nil)
 	C.git_diff_free(diff.ptr)
+	diff.ptr = nil
 	return nil
 }
 
diff --git a/patch.go b/patch.go
index 880f088..d927109 100644
--- a/patch.go
+++ b/patch.go
@@ -31,6 +31,7 @@ func (patch *Patch) Free() error {
 	}
 	runtime.SetFinalizer(patch, nil)
 	C.git_patch_free(patch.ptr)
+	patch.ptr = nil
 	return nil
 }