--- a/modules/libimg/png/mozpngconf.h
+++ b/modules/libimg/png/mozpngconf.h
@@ -61,16 +61,17 @@
 #define PNG_NO_READ_hIST
 #define PNG_NO_READ_pCAL
 #define PNG_NO_READ_pHYs
 #define PNG_NO_READ_sBIT
 #define PNG_NO_READ_sCAL
 #define PNG_NO_READ_sPLT
 #define PNG_NO_READ_TEXT
 #define PNG_NO_READ_tIME
+#define PNG_NO_READ_UNKNOWN_CHUNKS
 #define PNG_NO_READ_USER_CHUNKS
 #define PNG_NO_READ_EMPTY_PLTE
 #define PNG_NO_READ_OPT_PLTE
 #define PNG_NO_READ_STRIP_ALPHA
 #define PNG_NO_READ_oFFs
 #define PNG_NO_SEQUENTIAL_READ_SUPPORTED
 
 #ifndef MOZ_PNG_WRITE