diff --git a/ext/-test-/bignum/depend b/ext/-test-/bignum/depend
index 947441064c..b3fba1ea34 100644
--- a/ext/-test-/bignum/depend
+++ b/ext/-test-/bignum/depend
@@ -1,3 +1,4 @@
+extconf.h: $(SRCS)
 $(OBJS): $(HDRS) $(ruby_headers)
 
 intpack.o: intpack.c $(top_srcdir)/internal.h
diff --git a/ext/-test-/debug/depend b/ext/-test-/debug/depend
index 3cbdbe5a26..fb46c351ba 100644
--- a/ext/-test-/debug/depend
+++ b/ext/-test-/debug/depend
@@ -1,2 +1,3 @@
+extconf.h: $(SRCS)
 init.o: $(HDRS) $(ruby_headers)
 inspector.o: $(HDRS) $(ruby_headers) $(hdrdir)/ruby/debug.h
diff --git a/ext/-test-/exception/depend b/ext/-test-/exception/depend
index 79b6c53f50..ceb532a66e 100644
--- a/ext/-test-/exception/depend
+++ b/ext/-test-/exception/depend
@@ -1,3 +1,4 @@
+extconf.h: $(SRCS)
 $(OBJS): $(HDRS) $(ruby_headers) \
   $(hdrdir)/ruby/encoding.h \
   $(hdrdir)/ruby/oniguruma.h
diff --git a/ext/-test-/string/depend b/ext/-test-/string/depend
index 86617ff289..9ee6ff0944 100644
--- a/ext/-test-/string/depend
+++ b/ext/-test-/string/depend
@@ -1,3 +1,4 @@
+extconf.h: $(SRCS)
 $(OBJS): $(HDRS) $(ruby_headers) \
   $(hdrdir)/ruby/encoding.h \
   $(hdrdir)/ruby/oniguruma.h