diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0412ecf9b61bfe9a364e0e14514be31019a1b2fd..c4d88f1869de228cc78670820d28b7e6b5890b29 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -49,7 +49,11 @@ if (NOT is_multi_config)
                 CACHE STRING "Choose the type of build." FORCE
                 )
     elseif (NOT CMAKE_BUILD_TYPE IN_LIST allowed_build_types)
-        message(FATAL_ERROR "Unknown build type: ${CMAKE_BUILD_TYPE}")
+      message(WARNING "Unknown build type '${CMAKE_BUILD_TYPE}'. "
+        "Defaulting to '${default_build_type}'")
+      set(CMAKE_BUILD_TYPE "${default_build_type}"
+        CACHE STRING "Choose the type of build." FORCE
+        )
     endif ()
 endif ()