diff --git a/include/internal/TestCPPAssertions.h b/include/internal/TestCPPAssertions.h
index 5b3bc34..c7b6fec 100644
--- a/include/internal/TestCPPAssertions.h
+++ b/include/internal/TestCPPAssertions.h
@@ -181,7 +181,7 @@ namespace TestCPP {
          *                          type.
          */
         static void assertNoThrows (
-            function<void()> shouldNotThrow,
+            const function<void()>& shouldNotThrow,
             const string& failureMessage =
                 "Should not have thrown anything!"
         );
diff --git a/include/internal/TestCPPTestCase.h b/include/internal/TestCPPTestCase.h
index 1a5326c..5e4b35f 100644
--- a/include/internal/TestCPPTestCase.h
+++ b/include/internal/TestCPPTestCase.h
@@ -342,7 +342,7 @@ namespace TestCPP {
          * @return The duration of the function run, in nanoseconds.
          */
         template<typename F, typename ...Args>
-        static nanoseconds duration (F func, Args&&... args)
+        static nanoseconds duration (const F& func, Args&&... args)
         {
             auto start = system_clock::now();
             func(forward<Args>(args)...);
diff --git a/src/TestCPPAssertions.cpp b/src/TestCPPAssertions.cpp
index 1ec0ac6..53d4eae 100644
--- a/src/TestCPPAssertions.cpp
+++ b/src/TestCPPAssertions.cpp
@@ -134,7 +134,7 @@ namespace TestCPP {
     }
 
     void Assertions::assertNoThrows (
-            function<void()> shouldNotThrow,
+            const function<void()>& shouldNotThrow,
             const string& failureMessage
         )
     {