diff --git a/modules/juce_core/text/juce_TextDiff.cpp b/modules/juce_core/text/juce_TextDiff.cpp
index 8a03318b74..91c0e43397 100644
--- a/modules/juce_core/text/juce_TextDiff.cpp
+++ b/modules/juce_core/text/juce_TextDiff.cpp
@@ -28,7 +28,8 @@
 
 struct TextDiffHelpers
 {
-    enum { minLengthToMatch = 3 };
+    enum { minLengthToMatch = 3,
+           maxLengthToScan = 128 * 1024 };
 
     struct StringRegion
     {
@@ -38,6 +39,8 @@ struct TextDiffHelpers
         StringRegion (const String::CharPointerType t, int s, int len) noexcept
             : text (t), start (s), length (len) {}
 
+        void incrementStart() noexcept  { ++text; ++start; --length; }
+
         String::CharPointerType text;
         int start, length;
     };
@@ -61,27 +64,26 @@ struct TextDiffHelpers
 
     static void diffSkippingCommonStart (TextDiff& td, StringRegion a, StringRegion b)
     {
-        String::CharPointerType sa (a.text);
-        String::CharPointerType sb (b.text);
-        const int maxLen = jmax (a.length, b.length);
-
-        for (int i = 0; i < maxLen; ++i, ++sa, ++sb)
+        for (;;)
         {
-            if (*sa != *sb)
-            {
-                diffRecursively (td, StringRegion (sa, a.start + i, a.length - i),
-                                     StringRegion (sb, b.start + i, b.length - i));
+            const juce_wchar ca = *a.text;
+            const juce_wchar cb = *b.text;
+
+            if (ca != cb || ca == 0)
                 break;
-            }
+
+            a.incrementStart();
+            b.incrementStart();
         }
+
+        diffRecursively (td, a, b);
     }
 
     static void diffRecursively (TextDiff& td, StringRegion a, StringRegion b)
     {
-        int indexA, indexB;
-        const int len = findLongestCommonSubstring (a.text, a.length,
-                                                    b.text, b.length,
-                                                    indexA, indexB);
+        int indexA = 0, indexB = 0;
+        const int len = findLongestCommonSubstring (a.text, a.length, indexA,
+                                                    b.text, b.length, indexB);
 
         if (len >= minLengthToMatch)
         {
@@ -103,22 +105,25 @@ struct TextDiffHelpers
         }
     }
 
-    static int findLongestCommonSubstring (String::CharPointerType a, const int lenA,
-                                           const String::CharPointerType b, const int lenB,
-                                           int& indexInA, int& indexInB)
+    static int findLongestCommonSubstring (String::CharPointerType a, const int lenA, int& indexInA,
+                                           String::CharPointerType b, const int lenB, int& indexInB) noexcept
     {
         if (lenA == 0 || lenB == 0)
             return 0;
 
-        HeapBlock<int> lines;
-        lines.calloc (2 + 2 * (size_t) lenB);
+        if (lenA > maxLengthToScan || lenB > maxLengthToScan)
+            return findCommonSuffix (a, lenA, indexInA,
+                                     b, lenB, indexInB);
+
+        const size_t scratchSpace = sizeof (int) * (2 + 2 * (size_t) lenB);
+        int* const lines = (int*) alloca (scratchSpace);
+        zeromem (lines, scratchSpace);
 
         int* l0 = lines;
         int* l1 = l0 + lenB + 1;
 
         int loopsWithoutImprovement = 0;
         int bestLength = 0;
-        indexInA = indexInB = 0;
 
         for (int i = 0; i < lenA; ++i)
         {
@@ -156,6 +161,25 @@ struct TextDiffHelpers
         indexInB -= bestLength - 1;
         return bestLength;
     }
+
+    static int findCommonSuffix (String::CharPointerType a, const int lenA, int& indexInA,
+                                 String::CharPointerType b, const int lenB, int& indexInB) noexcept
+    {
+        int length = 0;
+        a += lenA - 1;
+        b += lenB - 1;
+
+        while (length < lenA && length < lenB && *a == *b)
+        {
+            --a;
+            --b;
+            ++length;
+        }
+
+        indexInA = lenA - length;
+        indexInB = lenB - length;
+        return length;
+    }
 };
 
 TextDiff::TextDiff (const String& original, const String& target)