diff --git a/system/jlib/jstring.cpp b/system/jlib/jstring.cpp
index 6e062d2938e..4048c887d4f 100644
--- a/system/jlib/jstring.cpp
+++ b/system/jlib/jstring.cpp
@@ -2869,36 +2869,24 @@ const char * stristr (const char *haystack, const char *needle)
     if (isEmptyString(haystack) || isEmptyString(needle))
         return nullptr;
 
-    const char *pptr  = needle;     /* Pattern to search for    */
-    const char *start = haystack;   /* Start with a bowl of hay */
-    const char *sptr;               /* Substring pointer        */
-    int   slen  = strlen(haystack); /* Total size of haystack   */
-    int   plen  = strlen(needle);   /* Length of our needle     */
-
-    /* while string length not shorter than pattern length */
-    for (; slen >= plen; start++, slen--)
+    const char * start = haystack;
+    size_t slen  = strlen(haystack); /* Total size of haystack   */
+    size_t nlen  = strlen(needle);   /* Length of our needle     */
+    char needle0 = tolower(*needle);
+    for (; slen >= nlen; start++, slen--)
     {
-        /* find start of pattern in string */
-        while (tolower(*start) != tolower(*needle))
-        {
-            start++;
-            slen--;
-            /* if pattern longer than string */
-            if (slen < plen)
-                return nullptr;
-        }
-
-        sptr = start;
-        pptr = (char *) needle;
-        while (tolower(*sptr) == tolower(*pptr))
+        if (tolower(*start) == needle0)
         {
-            sptr++;
-            pptr++;
-            /* if end of pattern then pattern was found */
-            if (!*pptr)
-                return start;
+            size_t i = 1;
+            for (;;)
+            {
+                if (i == nlen)
+                    return start;
+                if (tolower(start[i]) != tolower(needle[i]))
+                    break;
+                i++;
+            }
         }
     }
-
     return nullptr;
 }
diff --git a/testing/unittests/jlibtests.cpp b/testing/unittests/jlibtests.cpp
index 9918b77c5ef..6aeb3e11f36 100644
--- a/testing/unittests/jlibtests.cpp
+++ b/testing/unittests/jlibtests.cpp
@@ -38,7 +38,7 @@
 
 #include "unittests.hpp"
 
-#define CPPUNIT_ASSERT_EQUAL_STR(x, y) CPPUNIT_ASSERT_EQUAL(std::string(x),std::string(y))
+#define CPPUNIT_ASSERT_EQUAL_STR(x, y) CPPUNIT_ASSERT_EQUAL(std::string(x ? x : ""),std::string(y ? y : ""))
 
 static const unsigned oneMinute = 60000; // msec
 
@@ -3830,4 +3830,31 @@ CPPUNIT_TEST_SUITE_NAMED_REGISTRATION( JLibSecretsTest, "JLibSecretsTest" );
 
 
 
+class JLibStringTest : public CppUnit::TestFixture
+{
+public:
+    CPPUNIT_TEST_SUITE(JLibStringTest);
+        CPPUNIT_TEST(testStristr);
+    CPPUNIT_TEST_SUITE_END();
+
+    void testStristr()
+    {
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("abc", "abc"), "abc");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("abc", "ABC"), "abc");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("x", "ABC"), "");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("abcdefgh", "A"), "abcdefgh");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("ABCDEFGH", "a"), "ABCDEFGH");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("abcdefgh", "E"), "efgh");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("ABCDEFGH", "e"), "EFGH");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("abcdefgh", "FGH"), "fgh");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("aabcdefgh", "ABC"), "abcdefgh");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("ababacz", "ABAC"), "abacz");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("", "ABC"), "");
+        CPPUNIT_ASSERT_EQUAL_STR(stristr("ABC", ""), "");
+    }
+};
+
+CPPUNIT_TEST_SUITE_REGISTRATION( JLibStringTest );
+CPPUNIT_TEST_SUITE_NAMED_REGISTRATION( JLibStringTest, "JLibStringTest" );
+
 #endif // _USE_CPPUNIT