diff --git a/Tests/test_file_dds.py b/Tests/test_file_dds.py
index 2f46ed77e..58447122e 100644
--- a/Tests/test_file_dds.py
+++ b/Tests/test_file_dds.py
@@ -196,6 +196,13 @@ def test__accept_false():
     assert not output
 
 
+def test_invalid_file():
+    invalid_file = "Tests/images/flower.jpg"
+
+    with pytest.raises(SyntaxError):
+        DdsImagePlugin.DdsImageFile(invalid_file)
+
+
 def test_short_header():
     """Check a short header"""
     with open(TEST_FILE_DXT5, "rb") as f:
diff --git a/Tests/test_file_ftex.py b/Tests/test_file_ftex.py
index 5447dc740..cae20fa46 100644
--- a/Tests/test_file_ftex.py
+++ b/Tests/test_file_ftex.py
@@ -16,6 +16,13 @@ def test_load_dxt1():
             assert_image_similar(im, target.convert("RGBA"), 15)
 
 
+def test_invalid_file():
+    invalid_file = "Tests/images/flower.jpg"
+
+    with pytest.raises(SyntaxError):
+        FtexImagePlugin.FtexImageFile(invalid_file)
+
+
 def test_constants_deprecation():
     for enum, prefix in {
         FtexImagePlugin.Format: "FORMAT_",
diff --git a/docs/example/DdsImagePlugin.py b/docs/example/DdsImagePlugin.py
index 272409416..29fefba16 100644
--- a/docs/example/DdsImagePlugin.py
+++ b/docs/example/DdsImagePlugin.py
@@ -210,7 +210,9 @@ class DdsImageFile(ImageFile.ImageFile):
     format_description = "DirectDraw Surface"
 
     def _open(self):
-        magic, header_size = struct.unpack("<II", self.fp.read(8))
+        if not _accept(self.fp.read(4)):
+            raise SyntaxError("not a DDS file")
+        (header_size,) = struct.unpack("<I", self.fp.read(4))
         if header_size != 124:
             raise OSError(f"Unsupported header size {repr(header_size)}")
         header_bytes = self.fp.read(header_size - 4)
diff --git a/src/PIL/DdsImagePlugin.py b/src/PIL/DdsImagePlugin.py
index 260924fca..3a04bdb5d 100644
--- a/src/PIL/DdsImagePlugin.py
+++ b/src/PIL/DdsImagePlugin.py
@@ -111,7 +111,9 @@ class DdsImageFile(ImageFile.ImageFile):
     format_description = "DirectDraw Surface"
 
     def _open(self):
-        magic, header_size = struct.unpack("<II", self.fp.read(8))
+        if not _accept(self.fp.read(4)):
+            raise SyntaxError("not a DDS file")
+        (header_size,) = struct.unpack("<I", self.fp.read(4))
         if header_size != 124:
             raise OSError(f"Unsupported header size {repr(header_size)}")
         header_bytes = self.fp.read(header_size - 4)
diff --git a/src/PIL/FtexImagePlugin.py b/src/PIL/FtexImagePlugin.py
index 8629dcf64..b264b7c50 100644
--- a/src/PIL/FtexImagePlugin.py
+++ b/src/PIL/FtexImagePlugin.py
@@ -94,7 +94,8 @@ class FtexImageFile(ImageFile.ImageFile):
     format_description = "Texture File Format (IW2:EOC)"
 
     def _open(self):
-        struct.unpack("<I", self.fp.read(4))  # magic
+        if not _accept(self.fp.read(4)):
+            raise SyntaxError("not a FTEX file")
         struct.unpack("<i", self.fp.read(4))  # version
         self._size = struct.unpack("<2i", self.fp.read(8))
         mipmap_count, format_count = struct.unpack("<2i", self.fp.read(8))