diff --git a/t/t4019-diff-wserror.sh b/t/t4019-diff-wserror.sh
index 3a3663fbcb..f6d1f1ebab 100755
--- a/t/t4019-diff-wserror.sh
+++ b/t/t4019-diff-wserror.sh
@@ -20,11 +20,27 @@ test_expect_success setup '
 
 blue_grep='7;34m' ;# ESC [ 7 ; 3 4 m
 
+printf "\033[%s" "$blue_grep" >check-grep
+if (grep "$blue_grep" <check-grep | grep "$blue_grep") >/dev/null 2>&1
+then
+	grep_a=grep
+elif (grep -a "$blue_grep" <check-grep | grep -a "$blue_grep") >/dev/null 2>&1
+then
+	grep_a='grep -a'
+else
+	grep_a=grep ;# expected to fail...
+fi
+rm -f check-grep
+
+prepare_output () {
+	git diff --color >output
+	$grep_a "$blue_grep" output >error
+	$grep_a -v "$blue_grep" output >normal
+}
+
 test_expect_success default '
 
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -37,9 +53,7 @@ test_expect_success default '
 test_expect_success 'without -trail' '
 
 	git config core.whitespace -trail
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -53,9 +67,7 @@ test_expect_success 'without -trail (attribute)' '
 
 	git config --unset core.whitespace
 	echo "F whitespace=-trail" >.gitattributes
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -69,9 +81,7 @@ test_expect_success 'without -space' '
 
 	rm -f .gitattributes
 	git config core.whitespace -space
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT normal >/dev/null &&
@@ -85,9 +95,7 @@ test_expect_success 'without -space (attribute)' '
 
 	git config --unset core.whitespace
 	echo "F whitespace=-space" >.gitattributes
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT normal >/dev/null &&
@@ -101,9 +109,7 @@ test_expect_success 'with indent-non-tab only' '
 
 	rm -f .gitattributes
 	git config core.whitespace indent,-trailing,-space
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight error >/dev/null &&
 	grep HT normal >/dev/null &&
@@ -117,9 +123,7 @@ test_expect_success 'with indent-non-tab only (attribute)' '
 
 	git config --unset core.whitespace
 	echo "F whitespace=indent,-trailing,-space" >.gitattributes
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight error >/dev/null &&
 	grep HT normal >/dev/null &&
@@ -133,9 +137,7 @@ test_expect_success 'with cr-at-eol' '
 
 	rm -f .gitattributes
 	git config core.whitespace cr-at-eol
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -149,9 +151,7 @@ test_expect_success 'with cr-at-eol (attribute)' '
 
 	git config --unset core.whitespace
 	echo "F whitespace=trailing,cr-at-eol" >.gitattributes
-	git diff --color >output
-	grep "$blue_grep" output >error
-	grep -v "$blue_grep" output >normal
+	prepare_output
 
 	grep Eight normal >/dev/null &&
 	grep HT error >/dev/null &&
@@ -195,7 +195,7 @@ test_expect_success 'color new trailing blank lines' '
 	git add x &&
 	{ echo a; echo; echo; echo; echo c; echo; echo; echo; echo; } >x &&
 	git diff --color x >output &&
-	cnt=$(grep "${blue_grep}" output | wc -l) &&
+	cnt=$($grep_a "${blue_grep}" output | wc -l) &&
 	test $cnt = 2
 '