diff --git a/CMakeLists.txt b/CMakeLists.txt
index a3f6f6b..8944894 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,6 +42,7 @@ if (ENABLE_CUSTOM_COMPILER_FLAGS)
         -Wdouble-promotion
         -Wparentheses
         -Wformat-overflow
+        -Wunused-macros
         )
 endif()
 
diff --git a/cJSON.c b/cJSON.c
index 314560b..6e8255a 100644
--- a/cJSON.c
+++ b/cJSON.c
@@ -208,7 +208,6 @@ typedef struct
 
 /* check if the given size is left to read in a given parse buffer (starting with 1) */
 #define can_read(buffer, size) ((buffer != NULL) && (((buffer)->offset + size) <= (buffer)->length))
-#define cannot_read(buffer, size) (!can_read(buffer, size))
 /* check if the buffer can be accessed at the given index (starting with 0) */
 #define can_access_at_index(buffer, index) ((buffer != NULL) && (((buffer)->offset + index) < (buffer)->length))
 #define cannot_access_at_index(buffer, index) (!can_access_at_index(buffer, index))