diff --git a/Makefile.am b/Makefile.am
index e1dfd32b..6043b2aa 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -30,7 +30,7 @@ AM_CPPFLAGS += -DDATADIR='"$(datadir)"' -DLIBEXECDIR='"$(libexecdir)"' \
 	-DG_LOG_DOMAIN=\"OSTree\" \
   -DOSTREE_GITREV='"$(OSTREE_GITREV)"' \
 	-DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_40 '-DGLIB_VERSION_MAX_ALLOWED=G_ENCODE_VERSION(2,50)' \
-	-DSOUP_VERSION_MIN_REQUIRED=SOUP_VERSION_2_40 -DSOUP_VERSION_MAX_ALLOWED=SOUP_VERSION_2_48
+	-DSOUP_VERSION_MIN_REQUIRED=SOUP_VERSION_2_40 '-DSOUP_VERSION_MAX_ALLOWED=G_ENCODE_VERSION(2,48)'
 AM_CFLAGS += -std=gnu99 $(WARN_CFLAGS)
 AM_DISTCHECK_CONFIGURE_FLAGS += \
 	--enable-gtk-doc \