diff --git a/glib/gutf8.c b/glib/gutf8.c
index ba0a0e731..bca3358c2 100644
--- a/glib/gutf8.c
+++ b/glib/gutf8.c
@@ -42,6 +42,10 @@
 #include "glibintl.h"
 #include "gvalgrind.h"
 
+#if g_macro__has_attribute(ifunc) && !defined(G_OS_WIN32)
+#define HAVE_WORKING_IFUNC_ATTRIBUTE 1
+#endif
+
 #define UTF8_COMPUTE(Char, Mask, Len)					      \
   if (Char < 128)							      \
     {									      \
@@ -1841,7 +1845,7 @@ g_utf8_validate_native (const char  *str,
   return *str == 0;
 }
 
-#if g_macro__has_attribute(ifunc) && !defined(G_OS_WIN32)
+#ifdef HAVE_WORKING_IFUNC_ATTRIBUTE
 /* The fast implementation of UTF-8 validation in `utf8_verify()` technically
  * uses undefined behaviour when the string length is not provided (i.e. when
  * it’s looking for a trailing nul terminator): when doing word-sized reads of
@@ -1882,14 +1886,19 @@ g_utf8_validate_valgrind (const char  *str,
   return g_utf8_validate_len (str, max_len, end);
 }
 
-static gboolean (*resolve_g_utf8_validate (void)) (const char *, gssize, const char **)
+typedef gboolean (*GUtf8ValidateFunc) (const char  *str,
+                                       gssize       max_len,
+                                       const char **end);
+
+static GUtf8ValidateFunc
+resolve_g_utf8_validate (void)
 {
   if (RUNNING_ON_VALGRIND)
     return g_utf8_validate_valgrind;
   else
     return g_utf8_validate_native;
 }
-#endif
+#endif  /* HAVE_WORKING_IFUNC_ATTRIBUTE */
 
 /**
  * g_utf8_validate:
@@ -1924,7 +1933,7 @@ gboolean
 g_utf8_validate (const char   *str,
                  gssize        max_len,
                  const gchar **end)
-#if g_macro__has_attribute(ifunc) && !defined(G_OS_WIN32)
+#ifdef HAVE_WORKING_IFUNC_ATTRIBUTE
   __attribute__((ifunc ("resolve_g_utf8_validate")));
 #else
 {
@@ -1960,6 +1969,38 @@ g_utf8_validate_len (const char   *str,
   return max_len == 0;
 }
 
+static gboolean
+g_str_is_ascii_native (const char *str)
+{
+  utf8_verify_ascii (&str, NULL);
+
+  return *str == 0;
+}
+
+#ifdef HAVE_WORKING_IFUNC_ATTRIBUTE
+/* See above comment about `ifunc` use for g_utf8_validate(). */
+static gboolean
+g_str_is_ascii_valgrind (const char *str)
+{
+  size_t len = strlen (str);
+
+  utf8_verify_ascii (&str, &len);
+
+  return *str == 0;
+}
+
+typedef gboolean (*GStrIsAsciiFunc) (const char *str);
+
+static GStrIsAsciiFunc
+resolve_g_str_is_ascii (void)
+{
+  if (RUNNING_ON_VALGRIND)
+    return g_str_is_ascii_valgrind;
+  else
+    return g_str_is_ascii_native;
+}
+#endif  /* HAVE_WORKING_IFUNC_ATTRIBUTE */
+
 /**
  * g_str_is_ascii:
  * @str: a string
@@ -1971,13 +2012,18 @@ g_utf8_validate_len (const char   *str,
  *
  * Since: 2.40
  */
+#if g_macro__has_attribute(no_sanitize_address)
+  __attribute__((no_sanitize_address))
+#endif
 gboolean
 g_str_is_ascii (const gchar *str)
+#ifdef HAVE_WORKING_IFUNC_ATTRIBUTE
+  __attribute__((ifunc ("resolve_g_str_is_ascii")));
+#else
 {
-  utf8_verify_ascii (&str, NULL);
-
-  return *str == 0;
+  return g_str_is_ascii_native (str);
 }
+#endif
 
 /**
  * g_unichar_validate: