diff --git a/shared/nm-utils/nm-macros-internal.h b/shared/nm-utils/nm-macros-internal.h
index bbdf50be71..a8f78e6d2d 100644
--- a/shared/nm-utils/nm-macros-internal.h
+++ b/shared/nm-utils/nm-macros-internal.h
@@ -59,6 +59,8 @@
 
 #define nm_auto(fcn) __attribute__ ((cleanup(fcn)))
 
+static inline int nm_close (int fd);
+
 /**
  * nm_auto_free:
  *
@@ -96,7 +98,7 @@ _nm_auto_close_impl (int *pfd)
 	if (*pfd >= 0) {
 		int errsv = errno;
 
-		(void) close (*pfd);
+		(void) nm_close (*pfd);
 		errno = errsv;
 	}
 }
@@ -1149,4 +1151,22 @@ nm_decode_version (guint version, guint *major, guint *minor, guint *micro)
 
 /*****************************************************************************/
 
+/**
+ * nm_close:
+ *
+ * Like close() but throws an assertion if the input fd is
+ * invalid.  Closing an invalid fd is a programming error, so
+ * it's better to catch it early.
+ */
+static inline int
+nm_close (int fd)
+{
+	if (fd >= 0) {
+		if (close (fd) == 0)
+			return 0;
+		nm_assert (errno != EBADF);
+	}
+	return -1;
+}
+
 #endif /* __NM_MACROS_INTERNAL_H__ */