Index: codec2-dev/CMakeLists.txt
===================================================================
--- codec2-dev/CMakeLists.txt	(revision 3026)
+++ codec2-dev/CMakeLists.txt	(working copy)
@@ -52,18 +52,21 @@
 endif()
 
 # Set default C++ flags.
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall")
-set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -g -O3 -std=gnu11")
+include(CheckCCompilerFlag)
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -g -O3")
+CHECK_C_COMPILER_FLAG("-std=gnu11" COMPILER_SUPPORTS_GNU11)
+if(COMPILER_SUPPORTS_GNU11)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu11")
+else()
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99")
+endif()
 # set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-unused-function")
 
 set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS}")
-set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS}")
 set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS}")
-set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS}")
 
 # -fPIC is implied on MinGW...
 if(NOT WIN32)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIC")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fPIC")
 endif()