diff --git a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
index b0d0c44823e6..5d468aed4233 100644
--- a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
+++ b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
@@ -57,12 +57,43 @@ public final class UTF8String implements Comparable<UTF8String>, Externalizable,
   public Object getBaseObject() { return base; }
   public long getBaseOffset() { return offset; }
 
-  private static int[] bytesOfCodePointInUTF8 = {2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
-    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
-    3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
-    4, 4, 4, 4, 4, 4, 4, 4,
-    5, 5, 5, 5,
-    6, 6};
+  /**
+   * A char in UTF-8 encoding can take 1-4 bytes depending on the first byte which
+   * indicates the size of the char. See Unicode standard in page 126, Table 3-6:
+   * http://www.unicode.org/versions/Unicode10.0.0/UnicodeStandard-10.0.pdf
+   *
+   * Binary    Hex          Comments
+   * 0xxxxxxx  0x00..0x7F   Only byte of a 1-byte character encoding
+   * 10xxxxxx  0x80..0xBF   Continuation bytes (1-3 continuation bytes)
+   * 110xxxxx  0xC0..0xDF   First byte of a 2-byte character encoding
+   * 1110xxxx  0xE0..0xEF   First byte of a 3-byte character encoding
+   * 11110xxx  0xF0..0xF7   First byte of a 4-byte character encoding
+   *
+   * As a consequence of the well-formedness conditions specified in
+   * Table 3-7 (page 126), the following byte values are disallowed in UTF-8:
+   *   C0–C1, F5–FF.
+   */
+  private static byte[] bytesOfCodePointInUTF8 = {
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x00..0x0F
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x10..0x1F
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x20..0x2F
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x30..0x3F
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x40..0x4F
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x50..0x5F
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x60..0x6F
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x70..0x7F
+    // Continuation bytes cannot appear as the first byte
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x80..0x8F
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x90..0x9F
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xA0..0xAF
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xB0..0xBF
+    0, 0, // 0xC0..0xC1 - disallowed in UTF-8
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // 0xC2..0xCF
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // 0xD0..0xDF
+    3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, // 0xE0..0xEF
+    4, 4, 4, 4, 4, // 0xF0..0xF4
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 // 0xF5..0xFF - disallowed in UTF-8
+  };
 
   private static final boolean IS_LITTLE_ENDIAN =
       ByteOrder.nativeOrder() == ByteOrder.LITTLE_ENDIAN;
@@ -187,8 +218,9 @@ public void writeTo(OutputStream out) throws IOException {
    * @param b The first byte of a code point
    */
   private static int numBytesForFirstByte(final byte b) {
-    final int offset = (b & 0xFF) - 192;
-    return (offset >= 0) ? bytesOfCodePointInUTF8[offset] : 1;
+    final int offset = b & 0xFF;
+    byte numBytes = bytesOfCodePointInUTF8[offset];
+    return (numBytes == 0) ? 1: numBytes; // Skip the first byte disallowed in UTF-8
   }
 
   /**
diff --git a/common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java b/common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
index 9b303fa5bc6c..7c34d419574e 100644
--- a/common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
+++ b/common/unsafe/src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java
@@ -58,8 +58,12 @@ private static void checkBasic(String str, int len) {
   @Test
   public void basicTest() {
     checkBasic("", 0);
-    checkBasic("hello", 5);
+    checkBasic("¡", 1); // 2 bytes char
+    checkBasic("ку", 2); // 2 * 2 bytes chars
+    checkBasic("hello", 5); // 5 * 1 byte chars
     checkBasic("大 千 世 界", 7);
+    checkBasic("︽﹋％", 3); // 3 * 3 bytes chars
+    checkBasic("\uD83E\uDD19", 1); // 4 bytes char
   }
 
   @Test
@@ -791,4 +795,21 @@ public void trimRightWithTrimString() {
     assertEquals(fromString("头"), fromString("头a???/").trimRight(fromString("数?/*&^%a")));
     assertEquals(fromString("头"), fromString("头数b数数 [").trimRight(fromString(" []数b")));
   }
+
+  @Test
+  public void skipWrongFirstByte() {
+    int[] wrongFirstBytes = {
+      0x80, 0x9F, 0xBF, // Skip Continuation bytes
+      0xC0, 0xC2, // 0xC0..0xC1 - disallowed in UTF-8
+      // 0xF5..0xFF - disallowed in UTF-8
+      0xF5, 0xF6, 0xF7, 0xF8, 0xF9,
+      0xFA, 0xFB, 0xFC, 0xFD, 0xFE, 0xFF
+    };
+    byte[] c = new byte[1];
+
+    for (int i = 0; i < wrongFirstBytes.length; ++i) {
+      c[0] = (byte)wrongFirstBytes[i];
+      assertEquals(fromBytes(c).numChars(), 1);
+    }
+  }
 }