diff --git a/src/testrender/optixraytracer.cpp b/src/testrender/optixraytracer.cpp
index 04d23ab4e4..5904bd8629 100644
--- a/src/testrender/optixraytracer.cpp
+++ b/src/testrender/optixraytracer.cpp
@@ -1072,7 +1072,7 @@ OptixRaytracer::processPrintfBuffer(void* buffer_data, size_t buffer_size)
                     switch (format[j]) {
                     case '%':
                         // seems like a silly to print a '%', but it keeps the logic parallel with the other cases
-                        dst += snprintf(&buffer[dst], BufferSize - dst,
+                        dst += snprintf(&buffer[dst], BufferSize - dst, "%s",
                                         fmt_string.c_str());
                         format_end_found = true;
                         break;
diff --git a/src/testshade/optixgridrender.cpp b/src/testshade/optixgridrender.cpp
index 4128c21807..ba36a1a8a7 100644
--- a/src/testshade/optixgridrender.cpp
+++ b/src/testshade/optixgridrender.cpp
@@ -874,7 +874,7 @@ OptixGridRenderer::processPrintfBuffer(void* buffer_data, size_t buffer_size)
                     switch (format[j]) {
                     case '%':
                         // seems like a silly to print a '%', but it keeps the logic parallel with the other cases
-                        dst += snprintf(&buffer[dst], BufferSize - dst,
+                        dst += snprintf(&buffer[dst], BufferSize - dst, "%s",
                                         fmt_string.c_str());
                         format_end_found = true;
                         break;