diff --git a/lib/matplotlib/tests/test_ft2font.py b/lib/matplotlib/tests/test_ft2font.py
index ee7c7cea3aac..105feb37fa2f 100644
--- a/lib/matplotlib/tests/test_ft2font.py
+++ b/lib/matplotlib/tests/test_ft2font.py
@@ -203,6 +203,31 @@ def test_ft2font_invalid_args(tmp_path):
         ft2font.FT2Font(file, _kerning_factor=123)
 
 
+def test_ft2font_oversized_read():
+    # A file object whose read() returns *more* bytes than requested is
+    # misbehaving: FreeType only sizes its buffer for the requested count, so
+    # an over-long read must be rejected rather than overflow the buffer or be
+    # silently truncated. Verify that such an object causes construction to
+    # fail loudly instead.
+    data = Path(fm.findfont('DejaVu Sans')).read_bytes()
+
+    class OversizedReader:
+        def __init__(self, data):
+            self._data = data
+
+        def seek(self, offset):
+            pass
+
+        def read(self, size):
+            # Ignore the requested size and hand back the whole file, which is
+            # far more than FreeType ever asks for. The initial read(0) probe
+            # in the constructor still gets an empty bytes object.
+            return self._data if size else b''
+
+    with pytest.raises(RuntimeError):
+        ft2font.FT2Font(OversizedReader(data))
+
+
 @pytest.mark.parametrize('name, size, skippable',
                          [('DejaVu Sans', 1, False), ('WenQuanYi Zen Hei', 3, True)])
 def test_ft2font_face_index(name, size, skippable):
diff --git a/src/ft2font_wrapper.cpp b/src/ft2font_wrapper.cpp
index 771f1db5a191..a8654ba1d8a3 100644
--- a/src/ft2font_wrapper.cpp
+++ b/src/ft2font_wrapper.cpp
@@ -453,6 +453,15 @@ read_from_file_callback(FT_Stream stream, unsigned long offset, unsigned char *b
         if (PyBytes_AsStringAndSize(read_result.ptr(), &tmpbuf, &n_read) == -1) {
             throw py::error_already_set();
         }
+        if ((unsigned long)n_read > count) {
+            // A well-behaved read() never returns more than the requested
+            // number of bytes.  FreeType only ever sized `buffer` for `count`
+            // bytes, so honoring an over-long read would overflow it.  Rather
+            // than silently truncate (which would feed FreeType corrupt data),
+            // signal a failed read so that FT_Open_Face -- and in turn the
+            // FT2Font constructor -- raises.
+            n_read = 0;
+        }
         memcpy(buffer, tmpbuf, n_read);
     } catch (py::error_already_set &eas) {
         eas.discard_as_unraisable(__func__);