diff --git a/src/common.h b/src/common.h
index 2b81dfbce..04775df06 100644
--- a/src/common.h
+++ b/src/common.h
@@ -699,4 +699,12 @@ const T *get_by_sorted_name(const wcstring &name, const T (&vals)[N]) {
     return get_by_sorted_name(name.c_str(), vals);
 }
 
+/// As established in 1ab81ab90d1a408702e11f081fdaaafa30636c31, iswdigit() is very slow under glibc,
+/// and does nothing more than establish whether or not the single specified character is in the
+/// range ('0','9').
+__attribute__((always_inline))
+bool inline iswdigit(const wchar_t c) {
+    return c >= L'0' && c <= L'9';
+}
+
 #endif  // FISH_COMMON_H