diff --git a/cmake/Assertion.cmake b/cmake/Assertion.cmake
index 54484b2..ce92d8e 100644
--- a/cmake/Assertion.cmake
+++ b/cmake/Assertion.cmake
@@ -44,6 +44,9 @@ function(assert)
       list(GET ARGUMENTS 2 RIGHT_VALUE)
 
       if(OPERATOR STREQUAL MATCHES)
+        if(DEFINED "${LEFT_VALUE}")
+          set(LEFT_VALUE "${${LEFT_VALUE}}")
+        endif()
         set(MESSAGE "expected string '${LEFT_VALUE}'${NOT_WORD} to match '${RIGHT_VALUE}'")
       elseif(OPERATOR STREQUAL STREQUAL)
         set(MESSAGE "expected string '${LEFT_VALUE}'${NOT_WORD} to be equal to '${RIGHT_VALUE}'")
diff --git a/test/cmake/AssertionTest.cmake b/test/cmake/AssertionTest.cmake
index f9b8e2e..39a0b3e 100644
--- a/test/cmake/AssertionTest.cmake
+++ b/test/cmake/AssertionTest.cmake
@@ -72,16 +72,31 @@ function("Directory path assertions")
 endfunction()
 
 function("Regular expression match assertions")
-  assert("some string" MATCHES "so.*ing")
-  assert(NOT "some string" MATCHES "so.*other.*ing")
+  set(STRING_VAR "some string")
+
+  assert(STRING_VAR MATCHES "so.*ing")
+  assert("${STRING_VAR}" MATCHES "so.*ing")
+
+  assert(NOT STRING_VAR MATCHES "so.*other.*ing")
+  assert(NOT "${STRING_VAR}" MATCHES "so.*other.*ing")
+
+  mock_message()
+    assert(STRING_VAR MATCHES "so.*other.*ing")
+  end_mock_message()
+  assert_message(FATAL_ERROR "expected string 'some string' to match 'so.*other.*ing'")
 
   mock_message()
-    assert("some string" MATCHES "so.*other.*ing")
+    assert("${STRING_VAR}" MATCHES "so.*other.*ing")
   end_mock_message()
   assert_message(FATAL_ERROR "expected string 'some string' to match 'so.*other.*ing'")
 
   mock_message()
-    assert(NOT "some string" MATCHES "so.*ing")
+    assert(NOT STRING_VAR MATCHES "so.*ing")
+  end_mock_message()
+  assert_message(FATAL_ERROR "expected string 'some string' not to match 'so.*ing'")
+
+  mock_message()
+    assert(NOT ${STRING_VAR} MATCHES "so.*ing")
   end_mock_message()
   assert_message(FATAL_ERROR "expected string 'some string' not to match 'so.*ing'")
 endfunction()