diff --git a/unit-tests/Makefile.am b/unit-tests/Makefile.am
index 97787162..c9dc16f7 100644
--- a/unit-tests/Makefile.am
+++ b/unit-tests/Makefile.am
@@ -7,9 +7,11 @@ MYLIBS = \
  $(LTLIBMULTITHREAD) $(LTLIBTHREAD) $(SERVENT_LIB) @INTL_MACOSX_LIBS@ \
  $(LIBS) $(CODE_COVERAGE_LIBS)
 
-AM_CFLAGS = $(WERROR_CFLAGS) $(WARN_CFLAGS) $(CODE_COVERAGE_CFLAGS)
+AM_CFLAGS = $(WERROR_CFLAGS) $(WARN_CFLAGS) $(CODE_COVERAGE_CFLAGS) -DMALLOC_RETURNS_NONNULL
 AM_CPPFLAGS = -I$(top_srcdir)/include/wget -I$(srcdir) -I$(top_builddir)/lib -I$(top_srcdir)/lib \
- -DWGETVER_FILE=\"$(top_builddir)/include/wget/wgetver.h\" $(CODE_COVERAGE_CPPFLAGS)
+ -DWGETVER_FILE=\"$(top_builddir)/include/wget/wgetver.h\" $(CODE_COVERAGE_CPPFLAGS) \
+ -DMALLOC_RETURNS_NONNULL
+
 LDADD = ../lib/libgnu.la ../libwget/libwget.la $(MYLIBS)
 
 BASE_OBJS = \