diff --git a/src/libsodium/Makefile.am b/src/libsodium/Makefile.am
index e63745a5..e8db8834 100644
--- a/src/libsodium/Makefile.am
+++ b/src/libsodium/Makefile.am
@@ -184,7 +184,7 @@ if HAVE_LD_OUTPUT_DEF
 libsodium_la_LDFLAGS += -Wl,--output-def,libsodium-$(DLL_VERSION).def
 defexecdir = $(bindir)
 defexec_DATA = libsodium-$(DLL_VERSION).def
-DISTCLEANFILES += $(defexec_DATA)
+DISTCLEANFILES = $(defexec_DATA)
 endif
 
 SUBDIRS = \