diff --git a/src/virt-viewer-util.c b/src/virt-viewer-util.c
index 069586a..9e52b87 100644
--- a/src/virt-viewer-util.c
+++ b/src/virt-viewer-util.c
@@ -521,6 +521,7 @@ displays_cmp(const void *p1, const void *p2, gpointer user_data)
     guint j = *(guint*)p2;
     GdkRectangle *m1 = g_hash_table_lookup(displays, GINT_TO_POINTER(i));
     GdkRectangle *m2 = g_hash_table_lookup(displays, GINT_TO_POINTER(j));
+    g_return_val_if_fail(m1 != NULL && m2 != NULL, 0);
     diff = m1->x - m2->x;
     if (diff == 0)
         diff = m1->y - m2->y;
@@ -571,6 +572,7 @@ virt_viewer_align_monitors_linear(GHashTable *displays)
         guint nth = sorted_displays[i];
         g_assert(nth < ndisplays);
         GdkRectangle *rect = g_hash_table_lookup(displays, GINT_TO_POINTER(nth));
+        g_return_if_fail(rect != NULL);
         rect->x = x;
         rect->y = 0;
         x += rect->width;
@@ -603,6 +605,7 @@ virt_viewer_shift_monitors_to_origin(GHashTable *displays)
     g_hash_table_iter_init(&iter, displays);
     while (g_hash_table_iter_next(&iter, NULL, &value)) {
         GdkRectangle *display = value;
+        g_return_if_fail(display != NULL);
         if (display->width > 0 && display->height > 0) {
             xmin = MIN(xmin, display->x);
             ymin = MIN(ymin, display->y);
diff --git a/tests/test-monitor-alignment.c b/tests/test-monitor-alignment.c
index 4d0bf9d..522483f 100644
--- a/tests/test-monitor-alignment.c
+++ b/tests/test-monitor-alignment.c
@@ -100,6 +100,24 @@ test_monitor_shift(void)
     const TestCase test_cases[] = {
         {
             0, {NULL}, {NULL}, 0, {NULL}
+        },{
+            1,
+            {NULL},
+            {NULL},
+            G_LOG_LEVEL_CRITICAL,
+            {"*assertion 'display != NULL' failed"}
+        },{
+            2,
+            {NULL, &rects[0]},
+            {NULL, &rects[0]},
+            G_LOG_LEVEL_CRITICAL,
+            {"*assertion 'display != NULL' failed"}
+        },{
+            2,
+            {&rects[2], NULL},
+            {&rects[2], NULL},
+            G_LOG_LEVEL_CRITICAL,
+            {"*assertion 'display != NULL' failed"}
         },{
             2,
             {&rects[0], &rects[0]},
@@ -139,6 +157,31 @@ test_monitor_align_linear(void)
     const TestCase test_cases[] = {
         {
             0, {NULL}, {NULL}, 0, {NULL}
+        },{
+            1,
+            {NULL},
+            {NULL},
+            G_LOG_LEVEL_CRITICAL,
+            {"*assertion 'rect != NULL' failed"}
+        },{
+            2,
+            {NULL, &rects[1]},
+            {NULL, &rects[1]},
+            G_LOG_LEVEL_CRITICAL,
+            {
+                "*displays_cmp: assertion 'm1 != NULL && m2 != NULL' failed",
+                "*assertion 'rect != NULL' failed"
+            }
+        },{
+            3,
+            {&rects[1], NULL, &rects[0]},
+            {&rects[3], NULL, &rects[0]},
+            G_LOG_LEVEL_CRITICAL,
+            {
+                "*displays_cmp: assertion 'm1 != NULL && m2 != NULL' failed",
+                "*displays_cmp: assertion 'm1 != NULL && m2 != NULL' failed",
+                "*assertion 'rect != NULL' failed"
+            }
         },{
             2,
             {&rects[0], &rects[1]},