diff --git a/src/main/java/org/apache/commons/lang3/StringUtils.java b/src/main/java/org/apache/commons/lang3/StringUtils.java
index fa92e285d..88614bbaa 100644
--- a/src/main/java/org/apache/commons/lang3/StringUtils.java
+++ b/src/main/java/org/apache/commons/lang3/StringUtils.java
@@ -3628,16 +3628,17 @@ public class StringUtils {
         boolean containsLowercase = false;
         final int sz = cs.length();
         for (int i = 0; i < sz; i++) {
+            char nowChar = cs.charAt(i);
+            if (Character.isUpperCase(nowChar)) {
+                containsUppercase = true;
+            } else if (Character.isLowerCase(nowChar)) {
+                containsLowercase = true;
+            }
             if (containsUppercase && containsLowercase) {
                 return true;
             }
-            if (Character.isUpperCase(cs.charAt(i))) {
-                containsUppercase = true;
-            } else if (Character.isLowerCase(cs.charAt(i))) {
-                containsLowercase = true;
-            }
         }
-        return containsUppercase && containsLowercase;
+        return false;
     }
 
     /**
diff --git a/src/test/java/org/apache/commons/lang3/StringUtilsIsMixedCaseTest.java b/src/test/java/org/apache/commons/lang3/StringUtilsIsMixedCaseTest.java
new file mode 100644
index 000000000..c69af49d1
--- /dev/null
+++ b/src/test/java/org/apache/commons/lang3/StringUtilsIsMixedCaseTest.java
@@ -0,0 +1,102 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.lang3;
+
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+/**
+ * Test to show the better performance of the new implementation of isMixedCase
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Thread)
+@Warmup(iterations = 5, time = 10)
+public class StringUtilsIsMixedCaseTest {
+
+    public static final String LOWER_CASE_LETTERS = "abcdefghijklmnopqrstuvwxyz";
+    public static final String END_MATCH = "at the enD";
+    public static final String Middle_MATCH = "at tHe Mid";
+    public static final String EARLY_MATCH = "At tHe beginning";
+
+    @Benchmark
+    public boolean newIsMixedCaseNoneMatch() {
+        return StringUtils.isMixedCase(LOWER_CASE_LETTERS);
+    }
+
+    @Benchmark
+    public boolean oldIsMixedCaseNoneMatch() {
+        return oldIsMixedCase(LOWER_CASE_LETTERS);
+    }
+
+    @Benchmark
+    public boolean newIsMixedCaseEndMatch() {
+        return StringUtils.isMixedCase(END_MATCH);
+    }
+
+    @Benchmark
+    public boolean oldIsMixedCaseEndMatch() {
+        return oldIsMixedCase(END_MATCH);
+    }
+
+    @Benchmark
+    public boolean newIsMixedCaseMiddleMatch() {
+        return StringUtils.isMixedCase(Middle_MATCH);
+    }
+
+    @Benchmark
+    public boolean oldIsMixedCaseMiddleMatch() {
+        return oldIsMixedCase(Middle_MATCH);
+    }
+
+    @Benchmark
+    public boolean newIsMixedCaseBeginningMatch() {
+        return StringUtils.isMixedCase(EARLY_MATCH);
+    }
+
+    @Benchmark
+    public boolean oldIsMixedCaseBeginningMatch() {
+        return oldIsMixedCase(EARLY_MATCH);
+    }
+
+    public static boolean oldIsMixedCase(final CharSequence cs) {
+        if (StringUtils.isEmpty(cs) || cs.length() == 1) {
+            return false;
+        }
+        boolean containsUppercase = false;
+        boolean containsLowercase = false;
+        final int sz = cs.length();
+        for (int i = 0; i < sz; i++) {
+            if (containsUppercase && containsLowercase) {
+                return true;
+            }
+            if (Character.isUpperCase(cs.charAt(i))) {
+                containsUppercase = true;
+            } else if (Character.isLowerCase(cs.charAt(i))) {
+                containsLowercase = true;
+            }
+        }
+        return containsUppercase && containsLowercase;
+    }
+}