diff --git a/testsuite/css/change/test-css-change.c b/testsuite/css/change/test-css-change.c
index 1d60f0bcff..24650fa4c2 100644
--- a/testsuite/css/change/test-css-change.c
+++ b/testsuite/css/change/test-css-change.c
@@ -77,7 +77,7 @@ load_ui_file (GFile *file, gboolean generate)
   ui_file = g_file_get_path (file);
 
   css_file = test_get_other_file (ui_file, ".css");
-  g_assert (css_file != NULL);
+  g_assert_nonnull (css_file);
 
   provider = gtk_css_provider_new ();
   gtk_css_provider_load_from_path (provider, css_file);
@@ -90,7 +90,7 @@ load_ui_file (GFile *file, gboolean generate)
   if (window == NULL)
     window = GTK_WIDGET (gtk_builder_get_object (builder, "window"));
 
-  g_assert (window != NULL);
+  g_assert_nonnull (window);
 
 
   output = NULL;
diff --git a/testsuite/css/data.c b/testsuite/css/data.c
index 978be0e55e..9cb3544de6 100644
--- a/testsuite/css/data.c
+++ b/testsuite/css/data.c
@@ -84,7 +84,7 @@ test_parse (gconstpointer data)
       g_assert_nonnull (bytes);
       g_assert_no_error (error);
       if (test->mimetype == NULL)
-        g_assert (mimetype == NULL);
+        g_assert_null (mimetype);
       else
         g_assert_cmpstr (mimetype, ==, test->mimetype);
 
diff --git a/testsuite/css/nodes/test-css-nodes.c b/testsuite/css/nodes/test-css-nodes.c
index a44c4e4508..d8dd50471e 100644
--- a/testsuite/css/nodes/test-css-nodes.c
+++ b/testsuite/css/nodes/test-css-nodes.c
@@ -80,7 +80,7 @@ load_ui_file (GFile *file, gboolean generate)
   builder = gtk_builder_new_from_file (ui_file);
   window = GTK_WIDGET (gtk_builder_get_object (builder, "window1"));
 
-  g_assert (window != NULL);
+  g_assert_nonnull (window);
 
   output = NULL;
   g_signal_connect (window, "map", G_CALLBACK (style_context_changed), &output);
diff --git a/testsuite/css/style/test-css-style.c b/testsuite/css/style/test-css-style.c
index 93367fc336..68e8bfefcf 100644
--- a/testsuite/css/style/test-css-style.c
+++ b/testsuite/css/style/test-css-style.c
@@ -97,7 +97,7 @@ load_ui_file (GFile *file, gboolean generate)
   ui_file = g_file_get_path (file);
 
   css_file = test_get_other_file (ui_file, ".css");
-  g_assert (css_file != NULL);
+  g_assert_nonnull (css_file);
 
   provider = gtk_css_provider_new ();
   gtk_css_provider_load_from_path (provider, css_file);
@@ -108,7 +108,7 @@ load_ui_file (GFile *file, gboolean generate)
   builder = gtk_builder_new_from_file (ui_file);
   window = GTK_WIDGET (gtk_builder_get_object (builder, "window1"));
 
-  g_assert (window != NULL);
+  g_assert_nonnull (window);
 
   output = NULL;
   g_signal_connect (window, "map", G_CALLBACK (style_context_changed), &output);
@@ -125,7 +125,7 @@ load_ui_file (GFile *file, gboolean generate)
     }
 
   reference_file = test_get_other_file (ui_file, ".nodes");
-  g_assert (reference_file != NULL);
+  g_assert_nonnull (reference_file);
 
   diff = diff_with_file (reference_file, output, -1, &error);
   g_assert_no_error (error);