Index: lib/sanitizer_common/sanitizer_common_interceptors.inc
===================================================================
--- lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -3221,8 +3221,13 @@
     if (sz < buflen) ++sz;
     COMMON_INTERCEPTOR_WRITE_RANGE(ctx, buf, sz);
   } else {
-    // GNU version.
-    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, res, REAL(strlen)(res) + 1);
+    // The GNU version may either return 'buf', in which case it has written
+    // a null-terminated string into the buffer, or it may return a pointer
+    // to some pre-existing immutable storage (namely sys_errlist). We only
+    // consider the former case to be a write.
+    if (res == buf) {
+      COMMON_INTERCEPTOR_WRITE_RANGE(ctx, res, REAL(strlen)(res) + 1);
+    }
   }
   return res;
 }