diff --git a/system/jlib/jstring.cpp b/system/jlib/jstring.cpp
index 14e26205c1f..1692c94aeef 100644
--- a/system/jlib/jstring.cpp
+++ b/system/jlib/jstring.cpp
@@ -1072,9 +1072,17 @@ StringBuffer & StringBuffer::replaceString(const char* oldStr, const char* newSt
         {
             if (memcmp(buffer, oldStr, oldlen) == 0)
             {
-                ensureCapacity(newlen);
-                memcpy(buffer, newStr, newlen);
-                curLen = newlen;
+                if (newlen <= curLen)
+                {
+                    memmove(buffer, newStr, newlen);
+                    curLen = newlen;
+                }
+                else
+                {
+                    ensureCapacity(newlen);
+                    memcpy(buffer, newStr, newlen);
+                    curLen = newlen;
+                }
             }
         }
         else
diff --git a/testing/unittests/jlibtests.cpp b/testing/unittests/jlibtests.cpp
index 53500b8ca15..19d2bfcf4bf 100644
--- a/testing/unittests/jlibtests.cpp
+++ b/testing/unittests/jlibtests.cpp
@@ -914,12 +914,22 @@ void testEncodeCSVColumn()
         source.replaceString("ab", "xxx");
         CPPUNIT_ASSERT_EQUAL_STR("xxxbxxxxxx", source.str());
 
-        // Search String has same length as source string and matches
+        // Search string has same length as source string and matches
         source.set("ababab");
         source.replaceString("ababab", "xxxxxx");
         CPPUNIT_ASSERT_EQUAL_STR("xxxxxx", source.str());
 
-        // Search String has same length as source string and does not match
+        // Search string has same length as source string and replace is smaller than source
+        source.set("ababab");
+        source.replaceString("ababab", "xxx");
+        CPPUNIT_ASSERT_EQUAL_STR("xxx", source.str());
+
+        // Search string has same length as source string and replace is larger than source
+        source.set("ababab");
+        source.replaceString("ababab", "xxxxxxxxx");
+        CPPUNIT_ASSERT_EQUAL_STR("xxxxxxxxx", source.str());
+
+        // Search string has same length as source string and does not match
         source.set("ababab");
         source.replaceString("ababac", "xxxxxx");
         CPPUNIT_ASSERT_EQUAL_STR("ababab", source.str());