diff --git a/glib/gmacros.h b/glib/gmacros.h
index d5b2f30c1..c686e8094 100644
--- a/glib/gmacros.h
+++ b/glib/gmacros.h
@@ -1239,11 +1239,9 @@
 #if G_GNUC_CHECK_VERSION(2, 0) && defined(__OPTIMIZE__)
 #define _G_BOOLEAN_EXPR_IMPL(uniq, expr)        \
  G_GNUC_EXTENSION ({                            \
-   int G_PASTE (_g_boolean_var_, uniq);         \
+   int G_PASTE (_g_boolean_var_, uniq) = 0;     \
    if (expr)                                    \
       G_PASTE (_g_boolean_var_, uniq) = 1;      \
-   else                                         \
-      G_PASTE (_g_boolean_var_, uniq) = 0;      \
    G_PASTE (_g_boolean_var_, uniq);             \
 })
 #define _G_BOOLEAN_EXPR(expr) _G_BOOLEAN_EXPR_IMPL (__COUNTER__, expr)
diff --git a/glib/tests/cxx.cpp b/glib/tests/cxx.cpp
index 4b4dd5800..e00ffd407 100644
--- a/glib/tests/cxx.cpp
+++ b/glib/tests/cxx.cpp
@@ -536,6 +536,25 @@ test_string_free (void)
   g_free (data);
 }
 
+#if G_CXX_STD_CHECK_VERSION(14)
+static constexpr gboolean
+g_likely_test_expr (void)
+{
+  if G_LIKELY (1 == 1)
+    {
+      return TRUE;
+    }
+}
+
+static void
+test_constexpr_var_init (void)
+{
+  g_test_message ("Test that G_LIKELY macro creates an initialized variable "
+                  "for compatibility with constexpr");
+  g_assert_true (g_likely_test_expr ());
+}
+#endif
+
 #ifdef G_OS_WIN32
 static void
 test_clear_com (void)
@@ -595,6 +614,10 @@ main (int argc, char *argv[])
   g_test_add_func ("/C++/string-append", test_string_append);
   g_test_add_func ("/C++/string-free", test_string_free);
 
+#if G_CXX_STD_CHECK_VERSION(14)
+  g_test_add_func ("/C++/constexpr-var-init", test_constexpr_var_init);
+#endif
+
 #ifdef G_OS_WIN32
   g_test_add_func ("/C++/test_clear_com", test_clear_com);
 #endif