diff --git a/cfg/gtk.cfg b/cfg/gtk.cfg
index 3aee2e2b1a2..e7119755b3e 100644
--- a/cfg/gtk.cfg
+++ b/cfg/gtk.cfg
@@ -3285,8 +3285,7 @@
     <returnValue type="gchar*"/>
     <arg nr="1" direction="out">
       <not-null/>
-      <not-uninit/>
-      <strz/>
+      <minsize type="argvalue" arg="2"/>
     </arg>
     <arg nr="2" direction="in">
       <not-bool/>
@@ -3299,7 +3298,7 @@
       <strz/>
       <formatstr/>
     </arg>
-    <arg nr="4" direction="in">
+    <arg nr="variadic" direction="in">
       <not-bool/>
       <not-uninit/>
     </arg>
diff --git a/test/cfg/gtk.c b/test/cfg/gtk.c
index b923135e2d9..015aa6a6a3d 100644
--- a/test/cfg/gtk.c
+++ b/test/cfg/gtk.c
@@ -655,3 +655,35 @@ int g_return_val_if_reached_test(const char *s) {
 
     return 0;
 }
+
+void g_ascii_formatd_test(double d)
+{
+    // g_ascii_formatd() writes the buffer and formats exactly one double
+    gchar buf[39];
+    g_ascii_formatd(buf, sizeof(buf), "%.2f", d);
+    g_print("%s", buf);
+
+    // cppcheck-suppress invalidPrintfArgType_sint
+    g_ascii_formatd(buf, sizeof(buf), "%d", d);
+    g_print("%s", buf);
+
+    gchar small[4];
+    // cppcheck-suppress bufferAccessOutOfBounds
+    g_ascii_formatd(small, sizeof(buf), "%.2f", d);
+    g_print("%s", small);
+}
+
+void g_ascii_formatd_format_test(const gchar *format, int i)
+{
+    gchar buf[39];
+    // cppcheck-suppress invalidFunctionArgBool
+    g_ascii_formatd(buf, sizeof(buf), format, i == 1);
+    g_print("%s", buf);
+
+    struct {
+        double x;
+    } s;
+    // cppcheck-suppress [uninitvar, uninitStructMember]
+    g_ascii_formatd(buf, sizeof(buf), format, s.x);
+    g_print("%s", buf);
+}