diff --git a/corsikaio/io.py b/corsikaio/io.py
index 4490883..a060781 100644
--- a/corsikaio/io.py
+++ b/corsikaio/io.py
@@ -81,19 +81,22 @@ def iter_blocks(f):
             buffer_size, = RECORD_MARKER.unpack(data)
 
         data = f.read(buffer_size)
-        if len(data) == 0:
-            if is_fortran_file:
+        if is_fortran_file:
+            if len(data) < buffer_size:
                 raise IOError("Read less bytes than expected, file seems to be truncated")
-            else:
+
+        else:
+            if len(data) == 0:
                 return
 
-        n_blocks = len(data) // BLOCK_SIZE_BYTES
+        n_blocks, rest = divmod(len(data), BLOCK_SIZE_BYTES)
+        if rest != 0:
+            raise IOError("Read less bytes than expected, file seems to be truncated")
+
         for block in range(n_blocks):
             start = block * BLOCK_SIZE_BYTES
             stop = start + BLOCK_SIZE_BYTES
             block = data[start:stop]
-            if len(block) < BLOCK_SIZE_BYTES:
-                raise IOError("Read less bytes than expected, file seems to be truncated")
             yield block
 
         # read trailing record marker
diff --git a/tests/test_io.py b/tests/test_io.py
index a235d13..676de3c 100644
--- a/tests/test_io.py
+++ b/tests/test_io.py
@@ -154,3 +154,17 @@ def test_versions():
 
             block = read_block(f, buffer_size)
             assert get_version(block, EVTH_VERSION_POSITION) == version
+
+
+
+@pytest.mark.parametrize("size", (100, 1000, 5000))
+def test_iter_blocks_truncated(size, tmp_path, dummy_file):
+    path = tmp_path / f"test_truncated_{size}.dat"
+
+    with path.open("wb") as out, dummy_file.open("rb") as infile:
+        out.write(infile.read(size))
+
+    with pytest.raises(IOError, match="file seems to be truncated"):
+        with path.open("rb") as f:
+            for _ in iter_blocks(f):
+                pass