diff --git a/ml.cpp b/ml.cpp
index bf20ab3..f02b0d2 100644
--- a/ml.cpp
+++ b/ml.cpp
@@ -636,6 +636,10 @@ std::string MlError::description() const {
 	return MlPerfMon::instance().callstack() + "error: the expression `" + cause->debug() + "` with message \"" + msg + "\"";
 }
 
+const char * MlError::what() const noexcept {
+	return msg;
+}
+
 void MlEnvironment::combine(MlEnvironment const &other) {
 	// Normally, I would use the `insert` method of the `map` class,
 	// but it doesn't overwrite previously declared values for keys.
@@ -1844,8 +1848,7 @@ MlValue sprintf(std::vector<MlValue> args, MlEnvironment &env) {
 	if (args.size() < 1 || args.size() > 2)
 		throw MlError(MlValue("sprintf", sprintf), env, args.size() > 2 ? TOO_MANY_ARGS : TOO_FEW_ARGS);
 
-	return MlValue::string(
-		    mini_sprintf(args[0].as_string(), args.size() == 2 ? args[1].as_list() : std::vector<MlValue>{}));
+	return MlValue::string(mini_sprintf(args[0].as_string(), args.size() == 2 ? args[1].as_list() : std::vector<MlValue>{}));
 }
 
 // >>> (map (lambda (x) (+ x 10)) '(1 2 3 4 5 6))
diff --git a/ml.h b/ml.h
index 5aac218..d6d2e84 100644
--- a/ml.h
+++ b/ml.h
@@ -81,6 +81,8 @@ public:
     // Get the printable error description.
     std::string description() const;
 
+    const char * what() const noexcept override;
+
 private:
     MlValue *cause;
     MlEnvironment env;