diff --git a/AK/StringUtils.cpp b/AK/StringUtils.cpp
index 70c09fe0080..b9aed9c9aad 100644
--- a/AK/StringUtils.cpp
+++ b/AK/StringUtils.cpp
@@ -388,6 +388,15 @@ Optional<size_t> find_last(StringView haystack, char needle)
     return {};
 }
 
+Optional<size_t> find_last_not(StringView haystack, char needle)
+{
+    for (size_t i = haystack.length(); i > 0; --i) {
+        if (haystack[i - 1] != needle)
+            return i - 1;
+    }
+    return {};
+}
+
 Vector<size_t> find_all(StringView haystack, StringView needle)
 {
     Vector<size_t> positions;
diff --git a/AK/StringUtils.h b/AK/StringUtils.h
index 0e5f143c370..aa9b2af73d3 100644
--- a/AK/StringUtils.h
+++ b/AK/StringUtils.h
@@ -74,6 +74,7 @@ StringView trim_whitespace(StringView string, TrimMode mode);
 Optional<size_t> find(StringView haystack, char needle, size_t start = 0);
 Optional<size_t> find(StringView haystack, StringView needle, size_t start = 0);
 Optional<size_t> find_last(StringView haystack, char needle);
+Optional<size_t> find_last_not(StringView haystack, char needle);
 Vector<size_t> find_all(StringView haystack, StringView needle);
 enum class SearchDirection {
     Forward,
diff --git a/AK/StringView.h b/AK/StringView.h
index 9eb09a10e25..4b8b974aa45 100644
--- a/AK/StringView.h
+++ b/AK/StringView.h
@@ -107,6 +107,7 @@ public:
     }
     [[nodiscard]] Optional<size_t> find(StringView needle, size_t start = 0) const { return StringUtils::find(*this, needle, start); }
     [[nodiscard]] Optional<size_t> find_last(char needle) const { return StringUtils::find_last(*this, needle); }
+    [[nodiscard]] Optional<size_t> find_last_not(char needle) const { return StringUtils::find_last_not(*this, needle); }
     // FIXME: Implement find_last(StringView) for API symmetry.
 
     [[nodiscard]] Vector<size_t> find_all(StringView needle) const;