diff --git a/advanced/Scripts/utils.sh b/advanced/Scripts/utils.sh
index 37516472..f655e56c 100755
--- a/advanced/Scripts/utils.sh
+++ b/advanced/Scripts/utils.sh
@@ -57,7 +57,11 @@ addKey(){
   # touch file to prevent grep error if file does not exist yet
   touch "${file}"
 
-  if ! grep -q "^${key}" "${file}"; then
+  # Match key against entire line, using both anchors. We assume
+  # that the file's keys never have bounding whitespace. Anchors
+  # are necessary to ensure the key is considered absent when it
+  # is a substring of another key present in the file.
+  if ! grep -q "^${key}$" "${file}"; then
     # Key does not exist, add it.
     echo "${key}" >> "${file}"
   fi
diff --git a/test/test_any_utils.py b/test/test_any_utils.py
index 5b4075d9..b3fabe6c 100644
--- a/test/test_any_utils.py
+++ b/test/test_any_utils.py
@@ -40,6 +40,26 @@ def test_key_addition_works(host):
     assert expected_stdout == output.stdout
 
 
+def test_key_addition_substr(host):
+    """Confirms addKey adds substring keys (no value) to a file"""
+    host.run(
+        """
+    source /opt/pihole/utils.sh
+    addKey "./testoutput" "KEY_ONE"
+    addKey "./testoutput" "KEY_O"
+    addKey "./testoutput" "KEY_TWO"
+    addKey "./testoutput" "Y_TWO"
+    """
+    )
+    output = host.run(
+        """
+    cat ./testoutput
+    """
+    )
+    expected_stdout = "KEY_ONE\nKEY_O\nKEY_TWO\nY_TWO\n"
+    assert expected_stdout == output.stdout
+
+
 def test_key_removal_works(host):
     """Confirms removeKey removes a key or key/value pair"""
     host.run(