diff -aur a/cmake/modules/GetGitRevisionDescription.cmake b/cmake/modules/GetGitRevisionDescription.cmake
--- a/cmake/modules/GetGitRevisionDescription.cmake	2020-01-09 05:36:54.000000000 +1100
+++ b/cmake/modules/GetGitRevisionDescription.cmake	2020-01-30 16:50:35.633034303 +1100
@@ -42,11 +42,12 @@
 function(get_git_head_revision _refspecvar _hashvar)
 	set(GIT_PARENT_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
 	set(GIT_DIR "${GIT_PARENT_DIR}/.git")
+	set(TOP_LEVEL_DIR "${CMAKE_SOURCE_DIR}")
 	while(NOT EXISTS "${GIT_DIR}")	# .git dir not found, search parent directories
 		set(GIT_PREVIOUS_PARENT "${GIT_PARENT_DIR}")
 		get_filename_component(GIT_PARENT_DIR ${GIT_PARENT_DIR} PATH)
-		if(GIT_PARENT_DIR STREQUAL GIT_PREVIOUS_PARENT)
-			# We have reached the root directory, we are not in git
+		if(GIT_PARENT_DIR STREQUAL TOP_LEVEL_DIR)
+			# We have reached the top of the source tree, we are not in git
 			set(${_refspecvar} "GITDIR-NOTFOUND" PARENT_SCOPE)
 			set(${_hashvar} "GITDIR-NOTFOUND" PARENT_SCOPE)
 			return()