diff --git a/external/openglcts/modules/glesext/tessellation_shader/esextcTessellationShaderIsolines.cpp b/external/openglcts/modules/glesext/tessellation_shader/esextcTessellationShaderIsolines.cpp
index 809acb7..e776b81 100644
--- a/external/openglcts/modules/glesext/tessellation_shader/esextcTessellationShaderIsolines.cpp
+++ b/external/openglcts/modules/glesext/tessellation_shader/esextcTessellationShaderIsolines.cpp
@@ -704,7 +704,10 @@
 			{
 				memcpy(&result.rendered_data[0], &rendered_data[0], rendered_data.size());
 			}
-			countIsolines(result);
+			if (result.rendered_data.size() > 0)
+			{
+				countIsolines(result);
+			}
 
 			/* Store the test run descriptor. */
 			m_test_results[test.vertex_spacing_mode].push_back(result);