diff --git a/.travis.yml b/.travis.yml
index 48a3d0d35fc08..fa7b50bccd01d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -22,7 +22,7 @@ notifications:
           - http://julia.mit.edu:8000/travis-hook
 before_install:
     - if [ `uname` = "Linux" ]; then
-        BUILDOPTS="USEGCC=1 LLVM_CONFIG=llvm-config-3.3 LLVM_LLC=llc-3.3 VERBOSE=1 USE_BLAS64=0";
+        BUILDOPTS="USEGCC=1 LLVM_CONFIG=llvm-config-3.3 LLVM_LLC=llc-3.3 VERBOSE=1 USE_BLAS64=0 WITH_GC_VERIFY=1";
         for lib in LLVM ZLIB SUITESPARSE ARPACK BLAS FFTW LAPACK GMP MPFR PCRE LIBUNWIND OPENLIBM RMATH; do
             export BUILDOPTS="$BUILDOPTS USE_SYSTEM_$lib=1";
         done;
diff --git a/Make.inc b/Make.inc
index 7b6725e5fd6b1..b068f465f34da 100644
--- a/Make.inc
+++ b/Make.inc
@@ -65,6 +65,9 @@ USE_LIBCPP = 0
 # assume we don't have LIBSSP support in our compiler, will enable later if likely true
 HAVE_SSP = 0
 
+# GC debugging options
+WITH_GC_VERIFY = 0
+
 # Prevent picking up $ARCH from the environment variables
 ARCH=
 
@@ -426,6 +429,11 @@ $(error "please install either GNU tar or bsdtar")
 endif
 endif
 
+ifeq ($(WITH_GC_VERIFY), 1)
+JCXXFLAGS += -DGC_VERIFY
+JCFLAGS += -DGC_VERIFY
+endif
+
 # ===========================================================================
 
 # Select the cpu architecture to target, or automatically detects the user's compiler
diff --git a/contrib/windows/msys_build.sh b/contrib/windows/msys_build.sh
index 16f6528f8b828..0a2174e326258 100755
--- a/contrib/windows/msys_build.sh
+++ b/contrib/windows/msys_build.sh
@@ -146,6 +146,7 @@ $SEVENZIP x -y $f >> get-deps.log
 echo 'override LLVM_CONFIG = $(JULIAHOME)/usr/bin/llvm-config' >> Make.user
 
 if [ -n "$APPVEYOR" ]; then
+  echo "override WITH_GC_VERIFY = 1" >> Make.user
   for i in make.exe touch.exe msys-intl-8.dll msys-iconv-2.dll; do
     f="/c/MinGW/msys/1.0/bin/$i"
     if [ -e $f ]; then
diff --git a/src/gc.c b/src/gc.c
index ca18e6f25ebc1..d01d8e10542c8 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -503,7 +503,8 @@ static void add_lostval_parent(jl_value_t* parent)
 
 
 #define verify_parent(ty, obj, slot, args...) do {                      \
-        if (*(jl_value_t**)(slot) == lostval && (obj) != lostval) {     \
+        if (*(jl_value_t**)(slot) == lostval &&                         \
+            (jl_value_t*)(obj) != lostval) {                            \
             jl_printf(JL_STDOUT, "Found parent %s 0x%lx at %s:%d\n",    \
                       ty, (uintptr_t)(obj), __FILE__, __LINE__);        \
             jl_printf(JL_STDOUT, "\tloc 0x%lx : ", (uintptr_t)(slot));  \
@@ -1944,12 +1945,11 @@ static arraylist_t bits_save[4];
 // freelist in pools
 static void clear_mark(int bits)
 {
-    size_t i;
-    pool_t* pool;
-    gcval_t* pv;
+    gcval_t *pv;
     if (!verifying) {
-    for(int i = 0; i < 4; i++)
-        bits_save[i].len = 0;
+        for (int i = 0;i < 4;i++) {
+            bits_save[i].len = 0;
+        }
     }
     void *current_heap = NULL;
     bigval_t *bigs[2];
diff --git a/src/options.h b/src/options.h
index 91015f0860192..44b333e251eed 100644
--- a/src/options.h
+++ b/src/options.h
@@ -47,7 +47,9 @@
 
 // GC_VERIFY force a full verification gc along with every quick gc to ensure no
 // reachable memory is freed
-//#define GC_VERIFY
+#ifndef GC_VERIFY
+// #define GC_VERIFY
+#endif
 
 // profiling options