diff --git a/ml.cpp b/ml.cpp
index 0c09547..f8c7b0b 100644
--- a/ml.cpp
+++ b/ml.cpp
@@ -1953,7 +1953,9 @@ MlValue thread_create(std::vector<MlValue> args, MlEnvironment &env) {
 	    try {
 		    for (size_t i = 0; i < args.size(); i++)
 			    MlValue acc = args[i].eval(env);
-	    } catch (std::exception &e) {
+		} catch (const MlError &e) {
+			std::cerr << "thread_create exception: " << e.description() << std::endl;
+		} catch (const std::exception &e) {
 		    std::cerr << "thread_create exception: " << e.what() << std::endl;
 		    throw e;
 	    }
@@ -2024,7 +2026,7 @@ MlValue try_block(std::vector<MlValue> args, MlEnvironment &env) {
 		cs_posisition = MlPerfMon::instance().get_callstack_position();
 		value = args[0].eval(env);
 		// catch block
-	} catch (std::exception &e) {
+	} catch (const std::exception &e) {
 		MlPerfMon::instance().restore_callstack_position(cs_posisition);
 		env.set("ml-exception", MlValue::string(e.what()));
 		value = args[1].eval(env);
@@ -2251,10 +2253,10 @@ void repl(MlEnvironment &env) {
 				tmp = run(input, env);
 				std::cout << " => " << tmp.debug() << std::endl;
 				code += input + "\n";
-			} catch (MlError &e) {
+			} catch (const MlError &e) {
 				std::cerr << e.description() << std::endl;
 				MlPerfMon::instance().clear_callstack();
-			} catch (std::exception &e) {
+			} catch (const std::exception &e) {
 				std::cerr << e.what() << std::endl;
 			}
 		}
@@ -2335,7 +2337,7 @@ int main(int argc, char *argv[]) {
 
 		return 0;
 
-	} catch (MlError &e) {
+	} catch (const MlError &e) {
 		std::cerr << e.description() << std::endl;
 	} catch (const std::exception &e) {
 		std::cerr << MlPerfMon::instance().callstack() << e.what() << std::endl;