diff --git a/scripts/test_lib.sh b/scripts/test_lib.sh
index 59369e11c..9b0e8648b 100644
--- a/scripts/test_lib.sh
+++ b/scripts/test_lib.sh
@@ -48,6 +48,47 @@ function log_success {
   >&2 echo -n -e "${COLOR_NONE}"
 }
 
+# From http://stackoverflow.com/a/12498485
+function relativePath {
+  # both $1 and $2 are absolute paths beginning with /
+  # returns relative path to $2 from $1
+  local source=$1
+  local target=$2
+
+  local commonPart=$source
+  local result=""
+
+  while [[ "${target#$commonPart}" == "${target}" ]]; do
+    # no match, means that candidate common part is not correct
+    # go up one level (reduce common part)
+    commonPart="$(dirname "$commonPart")"
+    # and record that we went back, with correct / handling
+    if [[ -z $result ]]; then
+      result=".."
+    else
+      result="../$result"
+    fi
+  done
+
+  if [[ $commonPart == "/" ]]; then
+    # special case for root (no common path)
+    result="$result/"
+  fi
+
+  # since we now have identified the common part,
+  # compute the non-common part
+  local forwardPart="${target#$commonPart}"
+
+  # and now stick all parts together
+  if [[ -n $result ]] && [[ -n $forwardPart ]]; then
+    result="$result$forwardPart"
+  elif [[ -n $forwardPart ]]; then
+    # extra slash removal
+    result="${forwardPart:1}"
+  fi
+
+  echo "$result"
+}
 
 ####   Discovery of files/packages within a go module #####
 
@@ -73,7 +114,7 @@ function pkgs_in_module {
 function run {
   local rpath
   local command
-  rpath=$(realpath "--relative-to=${ETCD_ROOT_DIR}" "${PWD}")
+  rpath=$(relativePath "${ETCD_ROOT_DIR}" "${PWD}")
   # Quoting all components as the commands are fully copy-parsable:
   command=("${@}")
   command=("${command[@]@Q}")