diff --git a/sharness.sh b/sharness.sh
index b6f2f08c7..722479152 100644
--- a/sharness.sh
+++ b/sharness.sh
@@ -20,7 +20,10 @@
 
 if test -n "${ZSH_VERSION-}"
 then
+	SHARNESS_SOURCE=$0
 	emulate sh -o POSIX_ARGZERO
+else
+	SHARNESS_SOURCE=${BASH_SOURCE-$0}
 fi
 
 # Public: Current version of Sharness.
@@ -40,7 +43,7 @@ SHARNESS_TEST_DIRECTORY=$(cd "$SHARNESS_TEST_DIRECTORY" && pwd) || exit 1
 export SHARNESS_TEST_DIRECTORY
 
 # shellcheck disable=SC3028
-: "${SHARNESS_TEST_SRCDIR:=$(cd "$(dirname "${BASH_SOURCE-$0}")" && pwd)}"
+: "${SHARNESS_TEST_SRCDIR:=$(cd "$(dirname "$SHARNESS_SOURCE")" && pwd)}"
 # Public: Source directory of test code and sharness library.
 # This directory may be different from the directory in which tests are
 # being run.