diff --git a/src/utils/str.nim b/src/utils/str.nim
index 794778e..67db94d 100644
--- a/src/utils/str.nim
+++ b/src/utils/str.nim
@@ -19,11 +19,14 @@ proc safeDelete*(str: string, slice: Slice[int]): string =
 func findAndDelete*(str: string, chars: set[char], start = 0, last = str.len - 1): string =
   ## Find the next instance of `chars` from `start`.
   ## When found delete characters until `last`.
-  let startChar = str.find(chars, start, last)
-  if startChar == -1:
-    str
-  else:
-    str.safeDelete(startChar..last)
+  # Prevent passing negative numbers (e.g.: initial parser)
+  if start >= 0 and last >= 0:
+    let startChar = str.find(chars, start, last)
+    if startChar == -1:
+      str
+    else:
+      str.safeDelete(startChar..last)
+  else: str
 
 func deleteAfterNewline*(str: string, start = 0): string =
   ## Delete string after next Newline from `start`.
diff --git a/tests/utils/test_str.nim b/tests/utils/test_str.nim
index b3d66ed..3b13a43 100644
--- a/tests/utils/test_str.nim
+++ b/tests/utils/test_str.nim
@@ -20,3 +20,4 @@ suite "utils/str":
     let t = "foo\nbar"
     check(t.deleteAfterNewline() == "foo")
     check(t.deleteAfterNewline(start = 4) == t)
+    check(t.deleteAfterNewline(start = -1) == t)