diff -ur icu.org/source/common/unicode/utf16.h icu/source/common/unicode/utf16.h
--- icu.org/source/common/unicode/utf16.h	2017-02-03 19:57:23.000000000 +0100
+++ icu/source/common/unicode/utf16.h	2017-04-21 22:05:57.414397617 +0200
@@ -321,6 +321,7 @@
         (s)[(i)++]=(uint16_t)(((c)&0x3ff)|0xdc00); \
     } else /* c>0x10ffff or not enough space */ { \
         (isError)=TRUE; \
+        (void)(isError); \
     } \
 }