diff --git a/src/parse.js b/src/parse.js
index 52c019c..85ad1f3 100644
--- a/src/parse.js
+++ b/src/parse.js
@@ -484,6 +484,11 @@ TimestampParser.parseFormatString = function parseFormatString(format){
             addCharacter(ch);
         }
     }
+    if(directive) throw new TimestampParseError(
+        "Found unterminated directive at the end of the format string.", {
+            format: formatString
+        }
+    );
     if(tokens.length && tokens[tokens.length - 1].string === "Z"){
         tokens.zuluTimezone = true;
     }
diff --git a/test/canary-test.js b/test/canary-test.js
index 4df340f..41220a4 100644
--- a/test/canary-test.js
+++ b/test/canary-test.js
@@ -973,6 +973,16 @@ function createTests(strtime){
                 message: `Failed with format "%Y-%m-%?": Unknown directive "%?".`,
             });
         });
+        this.test("unterminated directive produces a readable error", function(){
+            assert.throws(() => strftime(new Date(), "%"), {
+                name: "TimestampParseError",
+                message: `Failed with format "%": Found unterminated directive at the end of the format string.`,
+            });
+            assert.throws(() => strptime("2000-01-01", "%"), {
+                name: "TimestampParseError",
+                message: `Failed with format "%": Found unterminated directive at the end of the format string.`,
+            });
+        });
         this.test("parse format is an empty string", function(){
             assert.throws(() => strptime("2000-01-01", ""), {
                 name: "TimestampParseError",