diff --git a/jetty-server/src/main/java/org/eclipse/jetty/server/MultiPartFormInputStream.java b/jetty-server/src/main/java/org/eclipse/jetty/server/MultiPartFormInputStream.java
index 492c52a12394..5d8eaffaa4ac 100644
--- a/jetty-server/src/main/java/org/eclipse/jetty/server/MultiPartFormInputStream.java
+++ b/jetty-server/src/main/java/org/eclipse/jetty/server/MultiPartFormInputStream.java
@@ -94,7 +94,7 @@ private enum State
     private volatile boolean _deleteOnExit;
     private volatile boolean _writeFilesWithFilenames;
     private volatile int _bufferSize = 16 * 1024;
-    private volatile State state = State.UNPARSED;
+    private State state = State.UNPARSED;
 
     public class MultiPart implements Part
     {
@@ -356,7 +356,11 @@ public String getContentDispositionFilename()
      */
     public MultiPartFormInputStream(InputStream in, String contentType, MultipartConfigElement config, File contextTmpDir)
     {
+        // Must be a multipart request.
         _contentType = contentType;
+        if (_contentType == null || !_contentType.startsWith("multipart/form-data"))
+            throw new IllegalArgumentException("content type is not multipart/form-data");
+
         _contextTmpDir =  (contextTmpDir != null) ? contextTmpDir : new File(System.getProperty("java.io.tmpdir"));
         _config = (config != null) ? config : new MultipartConfigElement(_contextTmpDir.getAbsolutePath());
 
@@ -520,10 +524,6 @@ protected void parse()
         MultiPartParser parser = null;
         try
         {
-            // if its not a multipart request, don't parse it
-            if (_contentType == null || !_contentType.startsWith("multipart/form-data"))
-                return;
-
             // sort out the location to which to write the files
             if (_config.getLocation() == null)
                 _tmpDir = _contextTmpDir;
diff --git a/jetty-server/src/test/java/org/eclipse/jetty/server/MultiPartFormInputStreamTest.java b/jetty-server/src/test/java/org/eclipse/jetty/server/MultiPartFormInputStreamTest.java
index 4854445e6be0..733bb7421516 100644
--- a/jetty-server/src/test/java/org/eclipse/jetty/server/MultiPartFormInputStreamTest.java
+++ b/jetty-server/src/test/java/org/eclipse/jetty/server/MultiPartFormInputStreamTest.java
@@ -206,12 +206,10 @@ public void testNonMultiPartRequest()
         throws Exception
     {
         MultipartConfigElement config = new MultipartConfigElement(_dirname, 1024, 3072, 50);
-        MultiPartFormInputStream mpis = new MultiPartFormInputStream(new ByteArrayInputStream(_multi.getBytes()),
-            "Content-type: text/plain",
-            config,
-            _tmpDir);
-        mpis.setDeleteOnExit(true);
-        assertTrue(mpis.getParts().isEmpty());
+        Throwable t = assertThrows(IllegalArgumentException.class, () ->
+            new MultiPartFormInputStream(new ByteArrayInputStream(_multi.getBytes()),
+                "Content-type: text/plain", config, _tmpDir));
+        assertThat(t.getMessage(), is("content type is not multipart/form-data"));
     }
 
     @Test