diff --git a/build/cmake/modules/InSourceBuild.cmake b/build/cmake/modules/InSourceBuild.cmake
index 4bc1a213..6953771d 100644
--- a/build/cmake/modules/InSourceBuild.cmake
+++ b/build/cmake/modules/InSourceBuild.cmake
@@ -6,24 +6,29 @@ function(prevent_in_source_build)
 	file(REAL_PATH "${CMAKE_SOURCE_DIR}" source_dir)
 	file(REAL_PATH "${CMAKE_BINARY_DIR}" binary_dir)
 	cmake_path(IS_PREFIX source_dir "${binary_dir}" result)
-	cmake_path(GET binary_dir FILENAME binary_dir_base)
 
 	# If an in-source build is in progress, and the build directory is not
 	# chosen in a very specific way, then stop the build.
-	if(result AND (NOT (binary_dir_base MATCHES "tmp*")))
-		message(FATAL_ERROR
-			"The use of an in-source build has been detected "
-			"(i.e., the binary directory specified to CMake is located "
-			"in or under the source directory).  "
-			"This can potentially trash the source tree.  "
-			"In fact, if you are seeing this message, you may have already "
-			"partially trashed the source tree.  "
-			"The use of an in-source build is not officially supported and "
-			"is therefore disallowed by default.  "
-			"If you like to live dangerously and would like to override "
-			"this default behavior, this can be accomplished via the "
-			"CMake option ALLOW_IN_SOURCE_BUILD."
-		)
+	if(result)
+		cmake_path(GET binary_dir FILENAME binary_dir_base)
+		if(NOT (binary_dir_base MATCHES "^tmp"))
+			message(FATAL_ERROR
+				"The use of an in-source build has been detected "
+				"(i.e., the binary directory specified to CMake is located "
+				"in or under the source directory).  "
+				"This can potentially trash the source tree.  "
+				"In fact, if you are seeing this message, you may have already "
+				"partially trashed the source tree.  "
+				"The use of an in-source build is not officially supported and "
+				"is therefore disallowed by default.  "
+				"If you like to live dangerously and would like to override "
+				"this default behavior, this can be accomplished via the "
+				"CMake option ALLOW_IN_SOURCE_BUILD.\n"
+				"CMake source directory: ${CMAKE_SOURCE_DIR}\n"
+				"CMake binary directory: ${CMAKE_BINARY_DIR}\n"
+				"CMake binary directory base: ${binary_dir_base}\n"
+			)
+		endif()
 	endif()
 
 endfunction()