diff --git a/check-compatibility.sh b/check-compatibility.sh
index f6930e7..966850c 100755
--- a/check-compatibility.sh
+++ b/check-compatibility.sh
@@ -48,7 +48,26 @@ CREATE EXTENSION crankshaft;
 \dx
 EOF
 
-# TODO save public functions and signatures
+# Save public function signatures
+psql $DBNAME <<'EOF'
+CREATE TABLE release_function_signatures AS
+  SELECT
+    p.proname as name,
+    pg_catalog.pg_get_function_result(p.oid) as result_type,
+    pg_catalog.pg_get_function_arguments(p.oid) as arguments,
+   CASE
+    WHEN p.proisagg THEN 'agg'
+    WHEN p.proiswindow THEN 'window'
+    WHEN p.prorettype = 'pg_catalog.trigger'::pg_catalog.regtype THEN 'trigger'
+    ELSE 'normal'
+   END as type
+  FROM pg_catalog.pg_proc p
+       LEFT JOIN pg_catalog.pg_namespace n ON n.oid = p.pronamespace
+  WHERE
+       n.nspname = 'cdb_crankshaft'
+       AND p.proname LIKE 'cdb_%'
+  ORDER BY 1, 2, 4;
+EOF
 
 # Deploy current dev branch
 make clean-dev || die "Could not clean dev files"
@@ -57,6 +76,33 @@ sudo make install || die "Could not deploy current dev branch"
 # Check it can be upgraded
 psql $DBNAME -c "ALTER EXTENSION crankshaft update to 'dev';" || die "Cannot upgrade to dev version"
 
+# Check against saved public function signatures
+psql $DBNAME <<'EOF'
+CREATE TABLE dev_function_signatures AS
+  SELECT
+    p.proname as name,
+    pg_catalog.pg_get_function_result(p.oid) as result_type,
+    pg_catalog.pg_get_function_arguments(p.oid) as arguments,
+   CASE
+    WHEN p.proisagg THEN 'agg'
+    WHEN p.proiswindow THEN 'window'
+    WHEN p.prorettype = 'pg_catalog.trigger'::pg_catalog.regtype THEN 'trigger'
+    ELSE 'normal'
+   END as type
+  FROM pg_catalog.pg_proc p
+       LEFT JOIN pg_catalog.pg_namespace n ON n.oid = p.pronamespace
+  WHERE
+       n.nspname = 'cdb_crankshaft'
+       AND p.proname LIKE 'cdb_%'
+  ORDER BY 1, 2, 4;
+EOF
 
+echo "Functions in development not in latest release (ok):"
+psql $DBNAME -c "SELECT * FROM dev_function_signatures EXCEPT SELECT * FROM release_function_signatures;"
 
-# TODO check against saved public functions and signatures
+echo "Functions in latest release not in development (compat issue):"
+psql $DBNAME -c "SELECT * FROM release_function_signatures EXCEPT SELECT * FROM dev_function_signatures;"
+
+# Fail if there's a signature mismatch / missing functions
+psql $DBNAME -c "SELECT * FROM release_function_signatures EXCEPT SELECT * FROM dev_function_signatures;" | fgrep '(0 rows)' \
+    || die "Function signatures changed"