diff --git a/release-notes/CREDITS-2.x b/release-notes/CREDITS-2.x
index d41734922a..72dda57f06 100644
--- a/release-notes/CREDITS-2.x
+++ b/release-notes/CREDITS-2.x
@@ -155,4 +155,7 @@ Doug Roper (htmldoug@github)
   * Suggested #463: Ensure that `skipChildren()` of non-blocking `JsonParser` will throw
     exception if not enough input
   (2.9.6)
- 
+
+Alexander Eyers-Taylor (aeyerstaylor@github)
+  * Reported #510: Fix ArrayIndexOutofBoundsException found by LGTM.com
+  (2.9.9)
diff --git a/release-notes/VERSION-2.x b/release-notes/VERSION-2.x
index 5145925401..ac205bf817 100644
--- a/release-notes/VERSION-2.x
+++ b/release-notes/VERSION-2.x
@@ -18,6 +18,8 @@ JSON library.
 
 #488: Fail earlier on coercions from "too big" `BigInteger` into
   fixed-size types (`int`, `long`, `short`)
+#510: Fix ArrayIndexOutofBoundsException found by LGTM.com
+ (reported by Alexander E-T)
 - Improve exception message for missing Base64 padding (see databind#2183)
 
 2.9.7 (19-Sep-2018)
diff --git a/src/main/java/com/fasterxml/jackson/core/json/ReaderBasedJsonParser.java b/src/main/java/com/fasterxml/jackson/core/json/ReaderBasedJsonParser.java
index 2c1f5a2303..f38e4aaedb 100644
--- a/src/main/java/com/fasterxml/jackson/core/json/ReaderBasedJsonParser.java
+++ b/src/main/java/com/fasterxml/jackson/core/json/ReaderBasedJsonParser.java
@@ -1960,7 +1960,7 @@ private String _handleOddName2(int startPtr, int hash, int[] codes) throws IOExc
             }
             char c = _inputBuffer[_inputPtr];
             int i = (int) c;
-            if (i <= maxCode) {
+            if (i < maxCode) {
                 if (codes[i] != 0) {
                     break;
                 }
diff --git a/src/test/java/com/fasterxml/jackson/core/read/NonStandardUnquotedNamesTest.java b/src/test/java/com/fasterxml/jackson/core/read/NonStandardUnquotedNamesTest.java
index d88d58856a..1aa75fff54 100644
--- a/src/test/java/com/fasterxml/jackson/core/read/NonStandardUnquotedNamesTest.java
+++ b/src/test/java/com/fasterxml/jackson/core/read/NonStandardUnquotedNamesTest.java
@@ -1,12 +1,18 @@
 package com.fasterxml.jackson.core.read;
 
 import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.core.JsonParseException;
 import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.core.JsonToken;
 
 public class NonStandardUnquotedNamesTest
     extends com.fasterxml.jackson.core.BaseTest
 {
+    private final JsonFactory UNQUOTED_FIELDS_F = new JsonFactory();
+    {
+        UNQUOTED_FIELDS_F.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
+    }
+
     public void testSimpleUnquotedBytes() throws Exception {
         _testSimpleUnquoted(MODE_INPUT_STREAM);
         _testSimpleUnquoted(MODE_INPUT_STREAM_THROTTLED);
@@ -16,7 +22,7 @@ public void testSimpleUnquotedBytes() throws Exception {
     public void testSimpleUnquotedChars() throws Exception {
         _testSimpleUnquoted(MODE_READER);
     }
-    
+
     public void testLargeUnquoted() throws Exception
     {
         _testLargeUnquoted(MODE_INPUT_STREAM);
@@ -25,12 +31,35 @@ public void testLargeUnquoted() throws Exception
         _testLargeUnquoted(MODE_READER);
     }
 
+    // [core#510]: ArrayIndexOutOfBounds
+    public void testUnquotedIssue510() throws Exception
+    {
+        // NOTE! Requires longer input buffer to trigger longer codepath
+        char[] fullChars = new char[4001];
+        for (int i = 0; i < 3998; i++) {
+             fullChars[i] = ' ';
+        }
+        fullChars[3998] = '{';
+        fullChars[3999] = 'a';
+        fullChars[4000] = 256;
+
+        JsonParser p = UNQUOTED_FIELDS_F.createParser(new java.io.StringReader(new String(fullChars)));
+        assertToken(JsonToken.START_OBJECT, p.nextToken());
+        try {
+            p.nextToken();
+            fail("Should not pass");
+        } catch (JsonParseException e) {
+            ; // should fail here
+        }
+        p.close();
+    }
+
     /*
     /****************************************************************
     /* Secondary test methods
     /****************************************************************
      */
-
+    
     private void _testLargeUnquoted(int mode) throws Exception
     {
         StringBuilder sb = new StringBuilder(5000);
@@ -51,9 +80,7 @@ private void _testLargeUnquoted(int mode) throws Exception
         }
         sb.append("]");
         String JSON = sb.toString();
-        JsonFactory f = new JsonFactory();
-        f.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
-        JsonParser p = createParser(f, mode, JSON);
+        JsonParser p = createParser(UNQUOTED_FIELDS_F, mode, JSON);
         assertToken(JsonToken.START_ARRAY, p.nextToken());
         for (int i = 0; i < REPS; ++i) {
             assertToken(JsonToken.START_OBJECT, p.nextToken());
@@ -68,11 +95,8 @@ private void _testLargeUnquoted(int mode) throws Exception
 
     private void _testSimpleUnquoted(int mode) throws Exception
     {
-        final JsonFactory f = new JsonFactory();
-        f.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
-
         String JSON = "{ a : 1, _foo:true, $:\"money!\", \" \":null }";
-        JsonParser p = createParser(f, mode, JSON);
+        JsonParser p = createParser(UNQUOTED_FIELDS_F, mode, JSON);
 
         assertToken(JsonToken.START_OBJECT, p.nextToken());
         assertToken(JsonToken.FIELD_NAME, p.nextToken());
@@ -98,7 +122,7 @@ private void _testSimpleUnquoted(int mode) throws Exception
         // Another thing, as per [Issue#102]: numbers
 
         JSON = "{ 123:true,4:false }";
-        p = createParser(f, mode, JSON);
+        p = createParser(UNQUOTED_FIELDS_F, mode, JSON);
 
         assertToken(JsonToken.START_OBJECT, p.nextToken());
         assertToken(JsonToken.FIELD_NAME, p.nextToken());