diff --git a/CMakeLists.txt b/CMakeLists.txt
index cf856238..cb3743fd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,11 +14,9 @@ set(CMAKE_LIBRARY_OUTPUT_DIRECTORY lib)
 set(CMAKE_C_FLAGS "-O2 -Wall -Wextra")
 set(CMAKE_C_FLAGS_DEBUG "-O0 -g -DDEBUG=1")
 
-option(USE_C11_FEATURE "Enable c11 feature" OFF)
-if(USE_C11_FEATURE)
-  add_definitions(-std=c11)
-else()
-  add_definitions(-std=c99)     # at least c99 is required
+option(STRICT_C89_MODE "Strict c89 mode" OFF)
+if(STRICT_C89_MODE)
+  add_definitions(-std=c89 -ansi -pedantic)
 endif()
 
 include_directories(extlib/benz/include)
diff --git a/extlib/benz/include/picrin/config.h b/extlib/benz/include/picrin/config.h
index 7a24f77e..6f0294be 100644
--- a/extlib/benz/include/picrin/config.h
+++ b/extlib/benz/include/picrin/config.h
@@ -39,10 +39,6 @@
 /* #define GC_DEBUG 1 */
 /* #define GC_DEBUG_DETAIL 1 */
 
-#if __STDC_VERSION__ < 199901L
-# error please activate c99 features
-#endif
-
 #ifndef PIC_DIRECT_THREADED_VM
 # if defined(__GNUC__) || defined(__clang__)
 #  define PIC_DIRECT_THREADED_VM 1