diff --git a/contrib/completion/git-prompt.sh b/contrib/completion/git-prompt.sh
index 054c52e90aeabb9a9ab5d4f9ee38b0799126b338..d3de80f60b3a2d42e0e684ca73443c4d36f6cc3f 100644
--- a/contrib/completion/git-prompt.sh
+++ b/contrib/completion/git-prompt.sh
@@ -124,7 +124,7 @@ __git_ps1_show_upstream ()
 			fi
 			;;
 		svn-remote.*.url)
-			svn_remote[ $((${#svn_remote[@]} + 1)) ]="$value"
+			svn_remote[$((${#svn_remote[@]} + 1))]="$value"
 			svn_url_pattern+="\\|$value"
 			upstream=svn+git # default upstream is SVN if available, else git
 			;;
@@ -146,10 +146,11 @@ __git_ps1_show_upstream ()
 	svn*)
 		# get the upstream from the "git-svn-id: ..." in a commit message
 		# (git-svn uses essentially the same procedure internally)
-		local svn_upstream=($(git log --first-parent -1 \
+		local -a svn_upstream
+		svn_upstream=($(git log --first-parent -1 \
 					--grep="^git-svn-id: \(${svn_url_pattern#??}\)" 2>/dev/null))
 		if [[ 0 -ne ${#svn_upstream[@]} ]]; then
-			svn_upstream=${svn_upstream[ ${#svn_upstream[@]} - 2 ]}
+			svn_upstream=${svn_upstream[${#svn_upstream[@]} - 2]}
 			svn_upstream=${svn_upstream%@*}
 			local n_stop="${#svn_remote[@]}"
 			for ((n=1; n <= n_stop; n++)); do