diff --git a/meson.build b/meson.build
index 8f3d0ce..99a3a80 100644
--- a/meson.build
+++ b/meson.build
@@ -15,7 +15,8 @@ project('libcamera', 'c', 'cpp',
 # git version tag, the build metadata (e.g. +211-c94a24f4) is omitted from
 # libcamera_git_version.
 libcamera_git_version = run_command('utils/gen-version.sh',
-                                    meson.source_root()).stdout().strip()
+                                    meson.source_root(),
+                                    meson.build_root()).stdout().strip()
 if libcamera_git_version == ''
     libcamera_git_version = meson.project_version()
 endif
diff --git a/utils/gen-version.sh b/utils/gen-version.sh
index 708c01d..8700479 100755
--- a/utils/gen-version.sh
+++ b/utils/gen-version.sh
@@ -3,7 +3,10 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 # Generate a version string using git describe
 
-if [ -n "$1" ]
+SRC_DIR="$1"
+BUILD_DIR="$2"
+
+if [ -n $SRC_DIR ]
 then
 	cd "$1" 2>/dev/null || exit 1
 fi
@@ -24,7 +27,11 @@ fi
 
 # Append a '-dirty' suffix if the working tree is dirty. Prevent false
 # positives due to changed timestamps by running git update-index.
-git update-index --refresh > /dev/null 2>&1
+if [ \( -n $SRC_DIR \) -a \( -n $BUILD_DIR \) -a
+     $(echo $BUILD_DIR | grep $SRC_DIR) ]
+then
+	git update-index --refresh > /dev/null 2>&1
+fi
 git diff-index --quiet HEAD || version="$version-dirty"
 
 # Replace first '-' with a '+' to denote build metadata, strip the 'g' in from