diff --git a/src/dock.c b/src/dock.c
index 5e7cc934..9d74b490 100644
--- a/src/dock.c
+++ b/src/dock.c
@@ -3015,9 +3015,9 @@ void wDockTrackWindowLaunch(WDock * dock, Window window)
 		wfree(command);
 
 	if (wm_class)
-		XFree(wm_class);
+		free(wm_class);
 	if (wm_instance)
-		XFree(wm_instance);
+		free(wm_instance);
 }
 
 void wClipUpdateForWorkspaceChange(WScreen * scr, int workspace)
diff --git a/src/properties.c b/src/properties.c
index 7279de12..46bc3caa 100644
--- a/src/properties.c
+++ b/src/properties.c
@@ -71,10 +71,13 @@ int PropGetWMClass(Window window, char **wm_class, char **wm_instance)
 		XFree(class_hint);
 		return False;
 	}
-	*wm_instance = class_hint->res_name;
-	*wm_class = class_hint->res_class;
+	*wm_instance = strdup(class_hint->res_name);
+	*wm_class = strdup(class_hint->res_class);
 
+	XFree(class_hint->res_name);
+	XFree(class_hint->res_class);
 	XFree(class_hint);
+
 	return True;
 }
 
diff --git a/src/session.c b/src/session.c
index 4a50f78a..811aee3b 100644
--- a/src/session.c
+++ b/src/session.c
@@ -257,9 +257,9 @@ static WMPropList *makeWindowState(WWindow * wwin, WApplication * wapp)
 	}
 
 	if (instance)
-		XFree(instance);
+		free(instance);
 	if (class)
-		XFree(class);
+		free(class);
 	if (command)
 		wfree(command);
 
diff --git a/src/window.c b/src/window.c
index bfc0ade4..7402b7de 100644
--- a/src/window.c
+++ b/src/window.c
@@ -830,9 +830,9 @@ WWindow *wManageWindow(WScreen *scr, Window window)
 			wwin->main_window = fPtr->leader;
 		}
 		if (instance)
-			XFree(instance);
+			free(instance);
 		if (class)
-			XFree(class);
+			free(class);
 #undef ADEQUATE
 	}
 
@@ -2654,9 +2654,9 @@ WMagicNumber wWindowGetSavedState(Window win)
 	if (command)
 		wfree(command);
 	if (instance)
-		XFree(instance);
+		free(instance);
 	if (class)
-		XFree(class);
+		free(class);
 
 	return wstate;
 }