diff --git a/CMake/CTestCustom.cmake.in b/CMake/CTestCustom.cmake.in
index 42d86fd47..9aadbfff1 100644
--- a/CMake/CTestCustom.cmake.in
+++ b/CMake/CTestCustom.cmake.in
@@ -80,7 +80,7 @@ set(CTEST_CUSTOM_WARNING_EXCEPTION
   "opencv/modules"
   # breathe / breathelink
   "Duplicate declaration"
-  "WARNING: Duplicate C\+\+ declaration"
+  "WARNING: Duplicate C\\+\\+ declaration"
 
   # Ignore clang's summary warning, assuming prior text has matched some
   # other warning expression: