diff --git a/contrib/pjdfstest/tests/ftruncate/12.t b/contrib/pjdfstest/tests/ftruncate/12.t
--- a/contrib/pjdfstest/tests/ftruncate/12.t
+++ b/contrib/pjdfstest/tests/ftruncate/12.t
@@ -22,7 +22,7 @@
 	;;
 *)
 	echo "not ok ${ntest}"
-	ntest=`expr ${ntest} + 1`
+	ntest=$((ntest + 1))
 	;;
 esac
 expect 0 unlink ${n0}
diff --git a/contrib/pjdfstest/tests/link/05.t b/contrib/pjdfstest/tests/link/05.t
--- a/contrib/pjdfstest/tests/link/05.t
+++ b/contrib/pjdfstest/tests/link/05.t
@@ -27,7 +27,7 @@
 	if [ $? -ne 0 ]; then
 		break
 	fi
-	i=`expr $i + 1`
+	i=$((i + 1))
 done
 test_check $i -eq ${link_max}
 
diff --git a/contrib/pjdfstest/tests/link/15.t b/contrib/pjdfstest/tests/link/15.t
--- a/contrib/pjdfstest/tests/link/15.t
+++ b/contrib/pjdfstest/tests/link/15.t
@@ -26,7 +26,7 @@
 	if [ $? -ne 0 ]; then
 		break
 	fi
-	i=`expr $i + 1`
+	i=$((i + 1))
 done
 expect ENOSPC link ${n0}/${n1} ${n0}/${n2}
 umount /dev/md${n}
diff --git a/contrib/pjdfstest/tests/mkdir/11.t b/contrib/pjdfstest/tests/mkdir/11.t
--- a/contrib/pjdfstest/tests/mkdir/11.t
+++ b/contrib/pjdfstest/tests/mkdir/11.t
@@ -24,7 +24,7 @@
 	if [ $? -ne 0 ]; then
 		break
 	fi
-	i=`expr $i + 1`
+	i=$((i + 1))
 done
 expect ENOSPC mkdir ${n0}/${n1} 0755
 umount /dev/md${n}
diff --git a/contrib/pjdfstest/tests/mkfifo/11.t b/contrib/pjdfstest/tests/mkfifo/11.t
--- a/contrib/pjdfstest/tests/mkfifo/11.t
+++ b/contrib/pjdfstest/tests/mkfifo/11.t
@@ -24,7 +24,7 @@
 	if [ $? -ne 0 ]; then
 		break
 	fi
-	i=`expr $i + 1`
+	i=$((i + 1))
 done
 expect ENOSPC mkfifo ${n0}/${n1} 0644
 umount /dev/md${n}
diff --git a/contrib/pjdfstest/tests/open/19.t b/contrib/pjdfstest/tests/open/19.t
--- a/contrib/pjdfstest/tests/open/19.t
+++ b/contrib/pjdfstest/tests/open/19.t
@@ -24,7 +24,7 @@
 	if [ $? -ne 0 ]; then
 		break
 	fi
-	i=`expr $i + 1`
+	i=$((i + 1))
 done
 expect ENOSPC open ${n0}/${i} O_RDONLY,O_CREAT 0644
 umount /dev/md${n}
diff --git a/contrib/pjdfstest/tests/symlink/11.t b/contrib/pjdfstest/tests/symlink/11.t
--- a/contrib/pjdfstest/tests/symlink/11.t
+++ b/contrib/pjdfstest/tests/symlink/11.t
@@ -24,7 +24,7 @@
 	if [ $? -ne 0 ]; then
 		break
 	fi
-	i=`expr $i + 1`
+	i=$((i + 1))
 done
 expect ENOSPC symlink test ${n0}/${n1}
 umount /dev/md${n}
diff --git a/contrib/pjdfstest/tests/truncate/12.t b/contrib/pjdfstest/tests/truncate/12.t
--- a/contrib/pjdfstest/tests/truncate/12.t
+++ b/contrib/pjdfstest/tests/truncate/12.t
@@ -22,7 +22,7 @@
 	;;
 *)
 	echo "not ok ${ntest}"
-	ntest=`expr ${ntest} + 1`
+	ntest=$((ntest + 1))
 	;;
 esac
 expect 0 unlink ${n0}