diff --git a/cmake/QtProcessConfigureArgs.cmake b/cmake/QtProcessConfigureArgs.cmake
index d7df9e142f6..1940b250fdb 100644
--- a/cmake/QtProcessConfigureArgs.cmake
+++ b/cmake/QtProcessConfigureArgs.cmake
@@ -590,7 +590,7 @@ while(1)
     endif()
 
     # Handle variable assignments
-    if(arg MATCHES "^([a-zA-Z0-9_-]+)=(.*)")
+    if(arg MATCHES "^([a-zA-Z0-9_][a-zA-Z0-9_-]*)=(.*)")
         list(APPEND cmake_var_assignments "${arg}")
         continue()
     endif()