diff --git a/patsy/contrasts.py b/patsy/contrasts.py
index 0ac9ac7..5f9cdbe 100644
--- a/patsy/contrasts.py
+++ b/patsy/contrasts.py
@@ -98,7 +98,7 @@ def t(obj, expected):
     # we can use "foo".encode here b/c this is python 3!
     # a utf-8 encoded euro-sign comes out as a real euro sign.
     t("\u20ac".encode("utf-8"), "\u20ac")
-    # but a iso-8859-15 euro sign can't be decoded, and we fall back on
+    # but an iso-8859-15 euro sign can't be decoded, and we fall back on
     # repr()
     t("\u20ac".encode("iso-8859-15"), "b'\\xa4'")
 
diff --git a/patsy/infix_parser.py b/patsy/infix_parser.py
index 6c127b5..1410a7f 100644
--- a/patsy/infix_parser.py
+++ b/patsy/infix_parser.py
@@ -11,7 +11,7 @@
 # Plus it spends energy on tracking where each item in the parse tree comes
 # from, to allow high-quality error reporting.
 #
-# You are expected to provide an collection of Operators, a collection of
+# You are expected to provide a collection of Operators, a collection of
 # atomic types, and an iterator that provides Tokens. Each Operator should
 # have a unique token_type (which is an arbitrary Python object), and each
 # Token should have a matching token_type, or one of the special types