diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2fffabf..706e5e2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -15,7 +15,7 @@ set(PROJECT_VERSION "${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}.${PROJECT
 option(ENABLE_CUSTOM_COMPILER_FLAGS "Enables custom compiler flags for Clang and GCC" ON)
 if (ENABLE_CUSTOM_COMPILER_FLAGS)
     if(("${CMAKE_C_COMPILER_ID}" MATCHES "GNU") OR ("${CMAKE_C_COMPILER_ID}" MATCHES "Clang"))
-        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c89 -pedantic -Wall -Wextra -Werror -Wstrict-prototypes -Wwrite-strings -Wshadow -Winit-self -Wcast-align -Wformat=2 -Wmissing-prototypes -Wstrict-overflow=2 -Wcast-qual -Wc++-compat")
+        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c89 -pedantic -Wall -Wextra -Werror -Wstrict-prototypes -Wwrite-strings -Wshadow -Winit-self -Wcast-align -Wformat=2 -Wmissing-prototypes -Wstrict-overflow=2 -Wcast-qual -Wc++-compat -Wundef")
     endif()
 endif()
 
diff --git a/Makefile b/Makefile
index 532cd99..b8a8e08 100644
--- a/Makefile
+++ b/Makefile
@@ -23,7 +23,7 @@ INSTALL_LIBRARY_PATH = $(DESTDIR)$(PREFIX)/$(LIBRARY_PATH)
 
 INSTALL ?= cp -a
 
-R_CFLAGS = -fPIC -std=c89 -pedantic -Wall -Werror -Wstrict-prototypes -Wwrite-strings -Wshadow -Winit-self -Wcast-align -Wformat=2 -Wmissing-prototypes -Wstrict-overflow=2 -Wcast-qual -Wc++-compat $(CFLAGS)
+R_CFLAGS = -fPIC -std=c89 -pedantic -Wall -Werror -Wstrict-prototypes -Wwrite-strings -Wshadow -Winit-self -Wcast-align -Wformat=2 -Wmissing-prototypes -Wstrict-overflow=2 -Wcast-qual -Wc++-compat -Wundef $(CFLAGS)
 
 uname := $(shell sh -c 'uname -s 2>/dev/null || echo false')
 
diff --git a/cJSON.c b/cJSON.c
index 80c0973..12e78cf 100644
--- a/cJSON.c
+++ b/cJSON.c
@@ -245,7 +245,7 @@ static int pow2gt (int x)
 #if INTEGER_SIZE & 0x1100 /* at least 32 bit */
     x |= x >> 16;
 #endif
-#if INT_SIZE & 0x1000 /* 64 bit */
+#if INTEGER_SIZE & 0x1000 /* 64 bit */
     x |= x >> 32;
 #endif