diff --git a/Modules/FindBISON.cmake b/Modules/FindBISON.cmake
index edde9eb96..7af336788 100644
--- a/Modules/FindBISON.cmake
+++ b/Modules/FindBISON.cmake
@@ -75,8 +75,9 @@ IF(BISON_EXECUTABLE)
     ELSEIF("${BISON_version_output}" MATCHES "^bison[^+]")
       STRING(REGEX REPLACE "^bison \\(GNU Bison\\) ([^\n]+)\n.*" "\\1"
         BISON_VERSION "${BISON_version_output}")
-    ELSE()
-      SET(BISON_VERSION "unknown")
+    ELSEIF("${BISON_version_output}" MATCHES "^GNU Bison ")
+      STRING(REGEX REPLACE "^GNU Bison (version )?([^\n]+).*" "\\2"
+        BISON_VERSION "${BISON_version_output}")
     ENDIF()
   ENDIF()