diff --git a/src/gallium/frontends/wgl/stw_tls.c b/src/gallium/frontends/wgl/stw_tls.c
index 0e8c177aa66..2a5d3cea477 100644
--- a/src/gallium/frontends/wgl/stw_tls.c
+++ b/src/gallium/frontends/wgl/stw_tls.c
@@ -306,7 +306,7 @@ stw_tls_get_data(void)
    }
 
    assert(data);
-   assert(data->dwThreadId = GetCurrentThreadId());
+   assert(data->dwThreadId == GetCurrentThreadId());
    assert(data->next == NULL);
 
    return data;