diff --git a/taglib/mp4/mp4atom.cpp b/taglib/mp4/mp4atom.cpp
index c4f4ff5d..02e90f9c 100644
--- a/taglib/mp4/mp4atom.cpp
+++ b/taglib/mp4/mp4atom.cpp
@@ -73,7 +73,7 @@ MP4::Atom::Atom(File *file)
     }
   }
 
-  if(length < 8) {
+  if(length < 8 || length > file->length() - offset) {
     debug("MP4: Invalid atom size");
     length = 0;
     file->seek(0, File::End);
@@ -81,6 +81,14 @@ MP4::Atom::Atom(File *file)
   }
 
   name = header.mid(4, 4);
+  for(int i = 0; i < 4; ++i) {
+    const char ch = name.at(i);
+    if((ch < ' ' || ch > '~') && ch != '\251') {
+      debug("MP4: Invalid atom type");
+      length = 0;
+      file->seek(0, File::End);
+    }
+  }
 
   for(int i = 0; i < numContainers; i++) {
     if(name == containers[i]) {
diff --git a/tests/data/ilst-is-last.m4a b/tests/data/ilst-is-last.m4a
index c56c8049..7f252ffd 100644
Binary files a/tests/data/ilst-is-last.m4a and b/tests/data/ilst-is-last.m4a differ
diff --git a/tests/test_mp4.cpp b/tests/test_mp4.cpp
index 14b23e1f..2ead2bab 100644
--- a/tests/test_mp4.cpp
+++ b/tests/test_mp4.cpp
@@ -575,7 +575,10 @@ public:
   void testFuzzedFile()
   {
     MP4::File f(TEST_FILE_PATH_C("infloop.m4a"));
-    CPPUNIT_ASSERT(f.isValid());
+    // The file has an invalid atom length of 2775 in the last atom
+    // ("free", offset 0xc521, 00000ad7 66726565), whereas the remaining file
+    // length is 2727 bytes, therefore the file is now considered invalid.
+    CPPUNIT_ASSERT(!f.isValid());
   }
 
   void testRepeatedSave()