And strengthened the uiControlType() test a bit.

common/controls.c

@@ -204,6 +204,15 @@ void *uiControlImplData(uiControl *c)
 	return c->implData;
 }
 
+static uiControl testHookControlWithInvalidControlMarker = {
+	.controlID = 5,
+};
+
+uiControl *uiprivTestHookControlWithInvalidControlMarker(void)
+{
+	return &testHookControlWithInvalidControlMarker;
+}
+
 static uiControl testHookControlWithInvalidType = {
 	.controlID = controlTypeID,
 	.typeID = 5,

common/testhooks.h

@@ -9,6 +9,7 @@ typedef void (*uiprivTestHookReportProgrammerErrorFunc)(const char *msg, void *d
 uiprivExtern void uiprivTestHookReportProgrammerError(uiprivTestHookReportProgrammerErrorFunc f, void *data);
 
 // controls.c
+uiprivExtern uiControl *uiprivTestHookControlWithInvalidControlMarker(void);
 uiprivExtern uiControl *uiprivTestHookControlWithInvalidType(void);
 
 #ifdef __cplusplus

test/controls_errors.cpp

@@ -64,12 +64,20 @@ static const struct checkErrorCase casesAfterOSVtable[] = {
 	{
 		"uiCheckControlType() with non-control",
 		[](void) {
-			static char buf[] = "this is not a uiControl";
+			// TODO make sure this is fine; if not, just use the following check instead
+			static char buf[] = "this is not a uiControl but is big enough to at the very least not cause a problem with UB hopefully";
 
 			uiCheckControlType(buf, uiControlType());
 		},
 		"uiCheckControlType(): object passed in not a uiControl",
 	},
+	{
+		"uiCheckControlType() with uiControl without uiControlType() marker",
+		[](void) {
+			uiCheckControlType(uiprivTestHookControlWithInvalidControlMarker(), uiControlType());
+		},
+		"uiCheckControlType(): object passed in not a uiControl",
+	},
 	{
 		"uiCheckControlType() with a control with an unknown type",
 		[](void) {