diff --git a/util/pure_concolic_execution.sh b/util/pure_concolic_execution.sh
index 34ba7a89..0c6d61c9 100755
--- a/util/pure_concolic_execution.sh
+++ b/util/pure_concolic_execution.sh
@@ -3,19 +3,20 @@
 set -u
 
 function usage() {
-    echo "Usage: $0 -i INPUT_DIR [-o OUTPUT_DIR] TARGET..."
+    echo "Usage: $0 -i INPUT_DIR [-o OUTPUT_DIR] [-f FAILED_DIR] TARGET..."
     echo
     echo "Run SymCC-instrumented TARGET in a loop, feeding newly generated inputs back "
     echo "into it. Initial inputs are expected in INPUT_DIR, and new inputs are "
     echo "continuously read from there. If OUTPUT_DIR is specified, a copy of the corpus "
     echo "and of each generated input is preserved there. TARGET may contain the special "
     echo "string \"@@\", which is replaced with the name of the current input file."
+    echo "If FAILED_DIR is specified, a copy of the failing test cases is preserved there."
     echo
     echo "Note that SymCC never changes the length of the input, so be sure that the "
     echo "initial inputs cover all required input lengths."
 }
 
-while getopts "i:o:" opt; do
+while getopts "i:o:f:" opt; do
     case "$opt" in
         i)
             in=$OPTARG
@@ -23,6 +24,9 @@ while getopts "i:o:" opt; do
         o)
             out=$OPTARG
             ;;
+        f)
+            failed_dir=$OPTARG
+            ;;
         *)
             usage
             exit 1
@@ -30,7 +34,9 @@ while getopts "i:o:" opt; do
     esac
 done
 shift $((OPTIND-1))
-target=$@
+target=("$@")
+target[0]=$(realpath "${target[0]}")
+target="${target[@]}"
 timeout="timeout -k 5 90"
 
 if [[ ! -v in ]]; then
@@ -46,13 +52,26 @@ touch $work_dir/analyzed_inputs
 if [[ -v out ]]; then
     mkdir -p $out
 fi
+if [[ -v failed_dir ]]; then
+    mkdir -p "$failed_dir"
+fi
 
 function cleanup() {
-    rm -rf $work_dir
+    rm -rf --preserve-root -- $work_dir
 }
 
 trap cleanup EXIT
 
+# Copy one file to the destination directory, renaming it according to its hash.
+function copy_file_with_unique_name() {
+  local file_name="$1"
+  local dest_dir="$2"
+
+  local dest="$dest_dir/$(sha256sum "$file_name" | cut -d' ' -f1)"
+  cp "$file_name" "$dest"
+
+}
+
 # Copy all files in the source directory to the destination directory, renaming
 # them according to their hash.
 function copy_with_unique_name() {
@@ -62,8 +81,7 @@ function copy_with_unique_name() {
     if [ -n "$(ls -A $source_dir)" ]; then
         local f
         for f in $source_dir/*; do
-            local dest="$dest_dir/$(sha256sum $f | cut -d' ' -f1)"
-            cp "$f" "$dest"
+          copy_file_with_unique_name "$f" "$dest_dir"
         done
     fi
 }
@@ -82,6 +100,17 @@ function maybe_export() {
     fi
 }
 
+# Remove input files which has been already analysed. Used to prevent infinite loop.
+function remove_analysed() {
+    local source_dir="$1"
+    local f
+    for f in $source_dir/*; do
+        if grep -q "$(basename $f)" $work_dir/analyzed_inputs; then
+            rm $f
+        fi
+    done
+}
+
 # Copy those files from the input directory to the next generation that haven't
 # been analyzed yet.
 function maybe_import() {
@@ -102,6 +131,15 @@ function maybe_import() {
     fi
 }
 
+# If the input file caused non 0 return code, then copy it to the FAILED_DIR.
+function save_failed() {
+  local ret_code=$1
+  local input_file="$2"
+  if [ $ret_code -ne 0 ] && [[ -v failed_dir ]] ; then
+    copy_file_with_unique_name "$input_file" "$failed_dir"
+  fi
+}
+
 # Set up the shell environment
 export SYMCC_OUTPUT_DIR=$work_dir/symcc_out
 export SYMCC_ENABLE_LINEARIZATION=1
@@ -123,13 +161,17 @@ while true; do
             echo "Running on $f"
             if [[ "$target " =~ " @@ " ]]; then
                 env SYMCC_INPUT_FILE=$f $timeout ${target[@]/@@/$f} >/dev/null 2>&1
+                ret_code=$?
             else
                 $timeout $target <$f >/dev/null 2>&1
+                ret_code=$?
             fi
 
             # Make the new test cases part of the next generation
             add_to_next_generation $work_dir/symcc_out
             maybe_export $work_dir/symcc_out
+            remove_analysed $work_dir/next
+            save_failed $ret_code "$f"
             echo $(basename $f) >> $work_dir/analyzed_inputs
             rm -f $f
         done