diff --git a/.travis.yml b/.travis.yml
index 1c7119dd..91a12da9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,12 +7,14 @@ addons:
   apt:
     packages:
       - gcc-multilib
+#     - valgrind
 env:
   - CFLAGS="-m32"
   - CFLAGS="-m64"
 script:
   - perl --version
   - make test
+# - make test-contrib TEST_RUNNER="valgrind -q --leak-check=full --dsymutil=yes --error-exitcode=1 bin/picrin"
   - make clean
   - make debug
   - make test
diff --git a/Makefile b/Makefile
index 809d867d..db9cf208 100644
--- a/Makefile
+++ b/Makefile
@@ -15,6 +15,8 @@ CONTRIB_INITS =
 CONTRIB_TESTS =
 CONTRIB_DOCS = $(wildcard contrib/*/docs/*.rst)
 
+TEST_RUNNER = bin/picrin
+
 CFLAGS += -I./extlib/benz/include -Wall -Wextra
 LDFLAGS += -lm
 
@@ -23,11 +25,11 @@ prefix = /usr/local
 all: CFLAGS += -O2 -DNDEBUG=1
 all: bin/picrin
 
-include $(sort $(wildcard contrib/*/nitro.mk))
-
 debug: CFLAGS += -O0 -g
 debug: bin/picrin
 
+include $(sort $(wildcard contrib/*/nitro.mk))
+
 bin/picrin: $(PICRIN_OBJS) $(CONTRIB_OBJS) lib/libbenz.a
 	$(CC) $(CFLAGS) -o $@ $(PICRIN_OBJS) $(CONTRIB_OBJS) lib/libbenz.a $(LDFLAGS)
 
diff --git a/contrib/10.macro/nitro.mk b/contrib/10.macro/nitro.mk
index a426ad2a..4d32cc3f 100644
--- a/contrib/10.macro/nitro.mk
+++ b/contrib/10.macro/nitro.mk
@@ -3,4 +3,4 @@ CONTRIB_LIBS += $(wildcard contrib/10.macro/*.scm)
 CONTRIB_TESTS += test-macro
 
 test-macro: bin/picrin
-	bin/picrin contrib/10.macro/t/ir-macro.scm
+	$(TEST_RUNNER) contrib/10.macro/t/ir-macro.scm
diff --git a/contrib/20.r7rs/nitro.mk b/contrib/20.r7rs/nitro.mk
index 9ddf756f..235a68c8 100644
--- a/contrib/20.r7rs/nitro.mk
+++ b/contrib/20.r7rs/nitro.mk
@@ -27,5 +27,5 @@ CONTRIB_TESTS += test-r7rs
 
 test-r7rs: bin/picrin
 	for test in `ls contrib/20.r7rs/t/*.scm`; do \
-	  bin/picrin "$$test"; \
+	  $(TEST_RUNNER) "$$test"; \
 	done
diff --git a/contrib/30.optional/nitro.mk b/contrib/30.optional/nitro.mk
index 78b4ade3..5711699f 100644
--- a/contrib/30.optional/nitro.mk
+++ b/contrib/30.optional/nitro.mk
@@ -3,5 +3,5 @@ CONTRIB_TESTS += test-optional
 
 test-optional: bin/picrin
 	for test in `ls contrib/30.optional/t/*.scm`; do \
-	  bin/picrin $$test; \
+	  $(TEST_RUNNER) $$test; \
 	done
diff --git a/contrib/30.random/nitro.mk b/contrib/30.random/nitro.mk
index a392fd17..043c23a8 100644
--- a/contrib/30.random/nitro.mk
+++ b/contrib/30.random/nitro.mk
@@ -4,5 +4,5 @@ CONTRIB_TESTS += test-random
 
 test-random: bin/picrin
 	for test in `ls contrib/30.random/t/*.scm`; do \
-	  bin/picrin $$test; \
+	  $(TEST_RUNNER) $$test; \
 	done
diff --git a/contrib/30.readline/nitro.mk b/contrib/30.readline/nitro.mk
index ec69703a..fe017e7a 100644
--- a/contrib/30.readline/nitro.mk
+++ b/contrib/30.readline/nitro.mk
@@ -12,5 +12,5 @@ contrib/src/readline.o: contrib/src/readline.c
 
 test-readline: bin/picrin
 	for test in `ls contrib/30.readline/t/*.scm`; do \
-	  bin/picrin $$test; \
+	  $(TEST_RUNNER) $$test; \
 	done
diff --git a/contrib/30.regexp/nitro.mk b/contrib/30.regexp/nitro.mk
index b96f5e59..3b10f016 100644
--- a/contrib/30.regexp/nitro.mk
+++ b/contrib/30.regexp/nitro.mk
@@ -4,5 +4,5 @@ CONTRIB_TESTS += test-regexp
 
 test-regexp: bin/picrin
 	for test in `ls contrib/30.regexp/t/*.scm`; do \
-	  bin/picrin $$test; \
+	  $(TEST_RUNNER) $$test; \
 	done
diff --git a/contrib/40.srfi/nitro.mk b/contrib/40.srfi/nitro.mk
index c939e570..e68b7a21 100644
--- a/contrib/40.srfi/nitro.mk
+++ b/contrib/40.srfi/nitro.mk
@@ -19,5 +19,5 @@ CONTRIB_TESTS += test-srfi
 
 test-srfi: bin/picrin
 	for test in `ls contrib/40.srfi/t/*.scm`; do \
-	  bin/picrin "$$test"; \
+	  $(TEST_RUNNER) "$$test"; \
 	done
diff --git a/contrib/50.for/nitro.mk b/contrib/50.for/nitro.mk
index 2ca63f23..ba5a25c5 100644
--- a/contrib/50.for/nitro.mk
+++ b/contrib/50.for/nitro.mk
@@ -3,5 +3,5 @@ CONTRIB_TESTS += test-for
 
 test-for: bin/picrin
 	for test in `ls contrib/50.for/t/*.scm`; do \
-	  bin/picrin "$$test"; \
+	  $(TEST_RUNNER) "$$test"; \
 	done
diff --git a/contrib/90.array/nitro.mk b/contrib/90.array/nitro.mk
index dc914f06..3d8a4770 100644
--- a/contrib/90.array/nitro.mk
+++ b/contrib/90.array/nitro.mk
@@ -3,4 +3,4 @@ CONTRIB_LIBS += $(wildcard contrib/90.array/*.scm)
 CONTRIB_TESTS += test-array
 
 test-array: bin/picrin
-	bin/picrin contrib/90.array/t/array.scm
+	$(TEST_RUNNER) contrib/90.array/t/array.scm
diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index fb2fa70f..5285f7ab 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -215,25 +215,25 @@ heap_free(pic_state *pic, void *ap)
 static void
 heap_morecore(pic_state *pic)
 {
-  union header *up, *np;
+  union header *bp, *np;
   struct heap_page *page;
-  size_t nu;
+  size_t nunits;
 
-  nu = PIC_HEAP_PAGE_SIZE / sizeof(union header);
+  nunits = PIC_HEAP_PAGE_SIZE / sizeof(union header);
 
-  assert(nu >= 2);
+  assert(nunits >= 2);
 
-  up = pic_malloc(pic, PIC_HEAP_PAGE_SIZE);
-  up->s.size = 0;               /* up is never used for allocation */
-  heap_free(pic, up + 1);
+  bp = pic_malloc(pic, PIC_HEAP_PAGE_SIZE);
+  bp->s.size = 0;               /* bp is never used for allocation */
+  heap_free(pic, bp + 1);
 
-  np = up + 1;
-  np->s.size = nu - 1;
+  np = bp + 1;
+  np->s.size = nunits - 1;
   heap_free(pic, np + 1);
 
   page = pic_malloc(pic, sizeof(struct heap_page));
-  page->basep = up;
-  page->endp = up + nu;
+  page->basep = bp;
+  page->endp = bp + nunits;
   page->next = pic->heap->pages;
 
   pic->heap->pages = page;