diff --git a/okonomiyaki/file_formats/_egg_info.py b/okonomiyaki/file_formats/_egg_info.py
index 6131fd0e..eba0396f 100644
--- a/okonomiyaki/file_formats/_egg_info.py
+++ b/okonomiyaki/file_formats/_egg_info.py
@@ -202,7 +202,7 @@ def text_or_none_attr(**kw):
 
 
 @six.python_2_unicode_compatible
-@attributes
+@attributes(frozen=True)
 class Requirement(object):
     """
     Model for entries in the package metadata inside EGG-INFO/spec/depend
diff --git a/okonomiyaki/platforms/_arch.py b/okonomiyaki/platforms/_arch.py
index 95783014..d5f53387 100644
--- a/okonomiyaki/platforms/_arch.py
+++ b/okonomiyaki/platforms/_arch.py
@@ -35,7 +35,7 @@ class ArchitectureKind(enum.Enum):
 }
 
 
-@attributes
+@attributes(frozen=True)
 class Arch(object):
     """ A normalized architecture representation.
     """
diff --git a/okonomiyaki/platforms/epd_platform.py b/okonomiyaki/platforms/epd_platform.py
index fec06467..6807e140 100644
--- a/okonomiyaki/platforms/epd_platform.py
+++ b/okonomiyaki/platforms/epd_platform.py
@@ -81,7 +81,7 @@ def wrapper(inst, attr, value):
 
 
 @six.python_2_unicode_compatible
-@attributes
+@attributes(frozen=True)
 class EPDPlatform(object):
     """
     An sane Canopy/EPD platform representation.
diff --git a/okonomiyaki/platforms/platform.py b/okonomiyaki/platforms/platform.py
index c4dfec6b..4b701b97 100644
--- a/okonomiyaki/platforms/platform.py
+++ b/okonomiyaki/platforms/platform.py
@@ -53,7 +53,7 @@ class NameKind(enum.Enum):
 
 
 @six.python_2_unicode_compatible
-@attributes(repr=False)
+@attributes(repr=False, frozen=True)
 class Platform(object):
     """
     An generic platform representation.