diff --git a/loopy/kernel/instruction.py b/loopy/kernel/instruction.py
index 564be622a48ffb44ce026da59e07189f811f557b..e6b0937856c45fd130f93742eb000c12921d0e11 100644
--- a/loopy/kernel/instruction.py
+++ b/loopy/kernel/instruction.py
@@ -417,7 +417,7 @@ class InstructionBase(ImmutableRecord):
 
     @property
     @memoize_method
-    def _key(self):
+    def _key_builder(self):
         from loopy.tools import LoopyEqKeyBuilder
         key_builder = LoopyEqKeyBuilder()
         key_builder.update_for_class(self.__class__)
@@ -433,7 +433,7 @@ class InstructionBase(ImmutableRecord):
             else:
                 key_builder.update_for_field(field_name, field_value)
 
-        return key_builder.key()
+        return key_builder
 
     def update_persistent_hash(self, key_hash, key_builder):
         """Custom hash computation function for use with
@@ -442,7 +442,7 @@ class InstructionBase(ImmutableRecord):
         Only works in conjunction with :class:`loopy.tools.KeyBuilder`.
         """
 
-        key_builder.rec(key_hash, self._key)
+        key_builder.rec(key_hash, self._key_builder.hash_key())
 
     # }}}
 
diff --git a/loopy/tools.py b/loopy/tools.py
index 30f4feefae976bd683f58b4caa0891334407349b..1ebbe5c8a4fd2b68e3bfcf5ed493384599dac2c5 100644
--- a/loopy/tools.py
+++ b/loopy/tools.py
@@ -152,10 +152,16 @@ class LoopyEqKeyBuilder(object):
         self.field_dict[field_name] = value
 
     def update_for_pymbolic_field(self, field_name, value):
-        self.field_dict[field_name] = str(value)
+        self.field_dict[field_name] = str(value).encode("utf-8")
 
     def key(self):
-        return (self.class_.__name__, self.field_dict)
+        return (self.class_.__name__.encode("utf-8"), self.field_dict)
+
+    def hash_key(self):
+        """Similar to key(), but excludes field names for faster hashing.
+        """
+        return (self.class_.__name__.encode("utf-8"),) + tuple(
+                self.field_dict[k] for k in sorted(self.field_dict.keys()))
 
 # }}}