diff --git a/.gitignore b/.gitignore
index a452215764..b72ddf0934 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
 /fuzz_corpora
 /fuzz-pack-headers
 /fuzz-pack-idx
+/GIT-BUILD-DIR
 /GIT-BUILD-OPTIONS
 /GIT-CFLAGS
 /GIT-LDFLAGS
diff --git a/Makefile b/Makefile
index 04d0fd1fe6..9347ed90da 100644
--- a/Makefile
+++ b/Makefile
@@ -3028,6 +3028,7 @@ else
 	@echo RUNTIME_PREFIX=\'false\' >>$@+
 endif
 	@if cmp $@+ $@ >/dev/null 2>&1; then $(RM) $@+; else mv $@+ $@; fi
+	@if test -f GIT-BUILD-DIR; then rm GIT-BUILD-DIR; fi
 
 ### Detect Python interpreter path changes
 ifndef NO_PYTHON
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index fe606c179f..29d7e236ae 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -1067,14 +1067,9 @@ endif()
 #Make the tests work when building out of the source tree
 get_filename_component(CACHE_PATH ${CMAKE_CURRENT_LIST_DIR}/../../CMakeCache.txt ABSOLUTE)
 if(NOT ${CMAKE_BINARY_DIR}/CMakeCache.txt STREQUAL ${CACHE_PATH})
-	file(RELATIVE_PATH BUILD_DIR_RELATIVE ${CMAKE_SOURCE_DIR} ${CMAKE_BINARY_DIR}/CMakeCache.txt)
-	string(REPLACE "/CMakeCache.txt" "" BUILD_DIR_RELATIVE ${BUILD_DIR_RELATIVE})
 	#Setting the build directory in test-lib.sh before running tests
 	file(WRITE ${CMAKE_BINARY_DIR}/CTestCustom.cmake
-		"file(STRINGS ${CMAKE_SOURCE_DIR}/t/test-lib.sh GIT_BUILD_DIR_REPL REGEX \"GIT_BUILD_DIR=(.*)\")\n"
-		"file(STRINGS ${CMAKE_SOURCE_DIR}/t/test-lib.sh content NEWLINE_CONSUME)\n"
-		"string(REPLACE \"\${GIT_BUILD_DIR_REPL}\" \"GIT_BUILD_DIR=\\\"$TEST_DIRECTORY/../${BUILD_DIR_RELATIVE}\\\"\" content \"\${content}\")\n"
-		"file(WRITE ${CMAKE_SOURCE_DIR}/t/test-lib.sh \${content})")
+		"file(WRITE ${CMAKE_SOURCE_DIR}/GIT-BUILD-DIR \"${CMAKE_BINARY_DIR}\")")
 	#misc copies
 	file(COPY ${CMAKE_SOURCE_DIR}/t/chainlint.sed DESTINATION ${CMAKE_BINARY_DIR}/t/)
 	file(COPY ${CMAKE_SOURCE_DIR}/po/is.po DESTINATION ${CMAKE_BINARY_DIR}/po/)
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 8cabb4d10f..a26a2c6147 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -47,6 +47,16 @@ then
 	echo "PANIC: Running in a $TEST_DIRECTORY that doesn't end in '/t'?" >&2
 	exit 1
 fi
+if test -f "$GIT_BUILD_DIR/GIT-BUILD-DIR"
+then
+	GIT_BUILD_DIR="$(cat "$GIT_BUILD_DIR/GIT-BUILD-DIR")" || exit 1
+	# On Windows, we must convert Windows paths lest they contain a colon
+	case "$(uname -s)" in
+	*MINGW*)
+		GIT_BUILD_DIR="$(cygpath -au "$GIT_BUILD_DIR")"
+		;;
+	esac
+fi
 
 # Prepend a string to a VAR using an arbitrary ":" delimiter, not
 # adding the delimiter if VAR or VALUE is empty. I.e. a generalized: