diff --git a/config.mk b/config.mk
index 44ec692..20bb2b2 100644
--- a/config.mk
+++ b/config.mk
@@ -26,7 +26,7 @@ CC = c99
 # CFLAGS, any additional compiler flags goes here
 CFLAGS = -Wall -pedantic -O2 -DNDEBUG
 # Uncomment for a debug build using gcc/clang
-# CFLAGS = -Wall -pedantic -g3 -fsanitize=address,undefined
+# CFLAGS = -Wall -pedantic -DDEBUG -g3 -fsanitize=address,undefined
 # LDFLAGS = $(CFLAGS)
 
 # icons that will be installed via `make icon`
diff --git a/nsxiv.h b/nsxiv.h
index 8011f9e..7e373c2 100644
--- a/nsxiv.h
+++ b/nsxiv.h
@@ -20,6 +20,10 @@
 #ifndef NSXIV_H
 #define NSXIV_H
 
+#if !defined(DEBUG) && !defined(NDEBUG)
+	#define NDEBUG
+#endif
+
 #include <stdbool.h>
 #include <stddef.h>