diff --git a/python_multipart/decoders.py b/python_multipart/decoders.py
index c4cdfb6..2e13858 100644
--- a/python_multipart/decoders.py
+++ b/python_multipart/decoders.py
@@ -142,8 +142,9 @@ def write(self, data: bytes) -> int:
         # If the last 2 characters have an '=' sign in it, then we won't be
         # able to decode the encoded value and we'll need to save it for the
         # next decoding step.
-        if data[-2:].find(b"=") != -1:
-            enc, rest = data[:-2], data[-2:]
+        idx = data.rfind(b"=", max(0, len(data) - 2))
+        if idx != -1:
+            enc, rest = data[:idx], data[idx:]
         else:
             enc = data
             rest = b""
diff --git a/tests/test_quoted_printable_chunks.py b/tests/test_quoted_printable_chunks.py
new file mode 100644
index 0000000..f520506
--- /dev/null
+++ b/tests/test_quoted_printable_chunks.py
@@ -0,0 +1,30 @@
+import binascii
+
+import pytest
+
+from python_multipart.decoders import QuotedPrintableDecoder
+
+
+class Sink:
+    def __init__(self) -> None:
+        self.b = b""
+
+    def write(self, data: bytes) -> int:
+        self.b += data
+        return len(data)
+
+
+@pytest.mark.parametrize(
+    "data",
+    [b"=41=42", b"a=41=42=43z", b"=41=\n=42", b"x=3D=3Dy"],
+)
+def test_chunked_matches_whole(data: bytes) -> None:
+    whole = binascii.a2b_qp(data)
+    for i in range(len(data) + 1):
+        for j in range(i, len(data) + 1):
+            sink = Sink()
+            decoder = QuotedPrintableDecoder(sink)
+            for part in (data[:i], data[i:j], data[j:]):
+                decoder.write(part)
+            decoder.finalize()
+            assert sink.b == whole, (i, j)