diff --git a/requirements.txt b/requirements.txt
index cc9ad37..a495e41 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,5 +2,5 @@ pyparsing>=2.1.0,<3
 olefile>=0.46
 easygui
 colorclass
-msoffcrypto-tool
+msoffcrypto-tool; platform_python_implementation!="PyPy" or platform_system!="Windows"
 pcodedmp>=1.2.5
\ No newline at end of file
diff --git a/setup.py b/setup.py
index 8cf6696..7c53562 100644
--- a/setup.py
+++ b/setup.py
@@ -321,7 +321,9 @@ def main():
             "olefile>=0.46",
             "easygui",
             'colorclass',
-            'msoffcrypto-tool',
+            # msoffcrypto-tool is not installable on PyPy+Windows (see issue #473),
+            # so we only require it if the platform is not Windows or not PyPy:
+            'msoffcrypto-tool; platform_python_implementation!="PyPy" or platform_system!="Windows"',
             'pcodedmp>=1.2.5',
         ],
     )