diff --git a/tests/compat.sh b/tests/compat.sh
index 2583d1bf5fdb..6895d6592eed 100755
--- a/tests/compat.sh
+++ b/tests/compat.sh
@@ -93,6 +93,8 @@ guess_config_name() {
 : ${MBEDTLS_TEST_OUTCOME_FILE=}
 : ${MBEDTLS_TEST_CONFIGURATION:="$(guess_config_name)"}
 : ${MBEDTLS_TEST_PLATFORM:="$(uname -s | tr -c \\n0-9A-Za-z _)-$(uname -m | tr -c \\n0-9A-Za-z _)"}
+# By default, we record the outcome to a new file
+append_outcome=0
 
 # default values for options
 # /!\ keep this synchronised with:
@@ -129,6 +131,7 @@ print_usage() {
     printf "  -v|--verbose\tSet verbose output.\n"
     printf "     --outcome-file\tFile where test outcomes are written\n"
     printf "                   \t(default: \$MBEDTLS_TEST_OUTCOME_FILE, none if empty)\n"
+    printf "     --append-outcome\tAppend records to the outcome file (if used)\n"
 }
 
 get_options() {
@@ -161,6 +164,9 @@ get_options() {
             --outcome-file)
                 shift; MBEDTLS_TEST_OUTCOME_FILE=$1
                 ;;
+            --append-outcome)
+                append_outcome=1
+                ;;
             -h|--help)
                 print_usage
                 exit 0
@@ -179,6 +185,20 @@ get_options() {
     TYPES="$( echo $TYPES | tr [a-z] [A-Z] )"
 }
 
+prepare_outcome_file() {
+    # Make the outcome file path relative to the original directory, not
+    # to .../tests
+    case "$MBEDTLS_TEST_OUTCOME_FILE" in
+        [!/]*)
+            MBEDTLS_TEST_OUTCOME_FILE="$ORIGINAL_PWD/$MBEDTLS_TEST_OUTCOME_FILE"
+            ;;
+    esac
+    # Should we write to a new outcome file?
+    if [ -n "$MBEDTLS_TEST_OUTCOME_FILE" ] && [ "$append_outcome" -eq 0 ]; then
+        rm -f "$MBEDTLS_TEST_OUTCOME_FILE"
+    fi
+}
+
 log() {
   if [ "X" != "X$VERBOSE" ]; then
     echo ""
@@ -971,14 +991,7 @@ run_client() {
 #
 
 get_options "$@"
-
-# Make the outcome file path relative to the original directory, not
-# to .../tests
-case "$MBEDTLS_TEST_OUTCOME_FILE" in
-    [!/]*)
-        MBEDTLS_TEST_OUTCOME_FILE="$ORIGINAL_PWD/$MBEDTLS_TEST_OUTCOME_FILE"
-        ;;
-esac
+prepare_outcome_file
 
 # sanity checks, avoid an avalanche of errors
 if [ ! -x "$M_SRV" ]; then