diff --git a/src/mesa/main/renderbuffer.c b/src/mesa/main/renderbuffer.c
index 3bb062bae2a..1fff668531a 100644
--- a/src/mesa/main/renderbuffer.c
+++ b/src/mesa/main/renderbuffer.c
@@ -1142,7 +1142,8 @@ _mesa_soft_renderbuffer_storage(GLcontext *ctx, struct gl_renderbuffer *rb,
 
    rb->Width = width;
    rb->Height = height;
-   rb->_BaseFormat = _mesa_base_fbo_format(ctx, rb->InternalFormat);
+   rb->_BaseFormat = _mesa_base_fbo_format(ctx, internalFormat);
+   ASSERT(rb->_BaseFormat);
 
    return GL_TRUE;
 }