diff --git a/projects/mercurial/Dockerfile b/projects/mercurial/Dockerfile
index 890c5237e..09b522093 100644
--- a/projects/mercurial/Dockerfile
+++ b/projects/mercurial/Dockerfile
@@ -18,7 +18,7 @@ FROM gcr.io/oss-fuzz-base/base-builder
 MAINTAINER security@mercurial-scm.org
 RUN apt-get update && apt-get install -y make autoconf automake libtool \
   python-dev mercurial curl
-RUN cd / && curl https://www.python.org/ftp/python/2.7.15/Python-2.7.15.tgz | tar xzf -
+RUN cd $SRC && curl https://www.python.org/ftp/python/2.7.15/Python-2.7.15.tgz | tar xzf -
 RUN hg clone https://www.mercurial-scm.org/repo/hg mercurial
 WORKDIR mercurial
 COPY build.sh $SRC/
diff --git a/projects/mercurial/build.sh b/projects/mercurial/build.sh
index 58d0670d9..30ee28137 100755
--- a/projects/mercurial/build.sh
+++ b/projects/mercurial/build.sh
@@ -15,8 +15,7 @@
 #
 ################################################################################
 
-pushd /Python-2.7.15/
-ls
+pushd $SRC/Python-2.7.15/
 patch -p1 <<'EOF'
 Index: v2_7_unstable/Python/pymath.c
 ===================================================================
@@ -46,8 +45,19 @@ Index: v2_7_unstable/Modules/_ctypes/callproc.c
      avalues = (void **)alloca(sizeof(void *) * argcount);
      atypes = (ffi_type **)alloca(sizeof(ffi_type *) * argcount);
 EOF
+
+if [ -e $OUT/sanpy/cflags -a "$(cat $OUT/sanpy/cflags)" = "${CFLAGS}" ] ; then
+    echo 'Python cflags unchanged, no need to rebuild'
+else
+    rm -rf $OUT/sanpy
+    ASAN_OPTIONS=detect_leaks=0 ./configure --without-pymalloc \
+                --prefix=$OUT/sanpy CFLAGS="${CFLAGS}" LINKCC="${CXX}" \
+                LDFLAGS="${CXXFLAGS}"
+    grep -v HAVE_GETC_UNLOCKED < pyconfig.h > tmp && mv tmp pyconfig.h
+    ASAN_OPTIONS=detect_leaks=0 make && make install
+    echo "${CFLAGS}" > $OUT/sanpy/cflags
+fi
 popd
 
 cd contrib/fuzz
-export PYLDFLAGS=$(echo $CFLAGS | xargs -n 1 echo | egrep -- '-fsanitize=(memory|address)')
-make oss-fuzz
+make clean oss-fuzz