diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
index 2afc65212..cfe1d6d7b 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
@@ -667,7 +667,7 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         for (CharSequence element : elements) {
             resultLength += element.length();
         }
-        resultLength += elements.length * delimiter.length();
+        resultLength += (elements.length - 1) * delimiter.length();
 
         char[] chars = new char[resultLength];
         int index = 0;
diff --git a/tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java b/tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java
index fb0eefff7..30ab6049a 100644
--- a/tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java
+++ b/tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java
@@ -290,4 +290,25 @@ public class StringTest {
     public void internsConstants() {
         assertSame("abc", ("a" + "bc").intern());
     }
+
+    @Test
+    public void joinStrings() {
+        String str = String.join("/", "a", "b");
+        assertEquals(3, str.length());
+        assertEquals("a/b", str);
+    }
+
+    @Test
+    public void joinSingleString() {
+        String str = String.join("/", "a");
+        assertEquals(1, str.length());
+        assertEquals("a", str);
+    }
+
+    @Test
+    public void joinNoStrings() {
+        String str = String.join("/");
+        assertEquals(0, str.length());
+        assertEquals("", str);
+    }
 }