diff --git a/pep-0509.txt b/pep-0509.txt
index 110fa1f10..8398bb1fe 100644
--- a/pep-0509.txt
+++ b/pep-0509.txt
@@ -38,9 +38,9 @@ The speedup of optimizations depends on the speed of guard checks. This
 PEP proposes to add a private version to dictionaries to implement fast
 guards on namespaces.
 
-Dictionary lookups can be skipped if the version does not change which
+Dictionary lookups can be skipped if the version does not change, which
 is the common case for most namespaces. The version is globally unique,
-so checking the version is also enough to check if the namespace
+so checking the version is also enough to verify that the namespace
 dictionary was not replaced with a new dictionary.
 
 When the dictionary version does not change, the performance of a guard
@@ -49,13 +49,14 @@ complexity is O(1).
 
 Example of optimization: copy the value of a global variable to function
 constants.  This optimization requires a guard on the global variable to
-check if it was modified. If the global variable is not modified, the
-function uses the cached copy. If the global variable is modified, the
-function uses a regular lookup, and maybe also deoptimize the function
-(to remove the overhead of the guard check for next function calls).
+check if it was modified after it was copied. If the global variable is
+not modified, the function uses the cached copy. If the global variable
+is modified, the function uses a regular lookup, and maybe also
+deoptimizes the function (to remove the overhead of the guard check for
+next function calls).
 
 See the `PEP 510 -- Specialized functions with guards
-<https://www.python.org/dev/peps/pep-0510/>`_ for the concrete usage of
+<https://www.python.org/dev/peps/pep-0510/>`_ for concrete usage of
 guards to specialize functions and for a more general rationale on
 Python static optimizers.
 
@@ -63,7 +64,7 @@ Python static optimizers.
 Guard example
 =============
 
-Pseudo-code of an fast guard to check if a dictionary entry was modified
+Pseudo-code of a fast guard to check if a dictionary entry was modified
 (created, updated or deleted) using an hypothetical
 ``dict_get_version(dict)`` function::
 
@@ -211,7 +212,7 @@ Example using an hypothetical ``dict_get_version(dict)`` function::
     103
 
 ``dict.__setitem__(key, value)`` and ``dict.update(...)`` always
-increases the version, even if the new value is identical or is equal to
+increase the version, even if the new value is identical or is equal to
 the current value (even if ``(dict[key] is value) or (dict[key] ==
 value)``).
 
@@ -259,7 +260,7 @@ Integer overflow
 
 The implementation uses the C type ``PY_UINT64_T`` to store the version:
 a 64 bits unsigned integer. The C code uses ``version++``. On integer
-overflow, the version is wrapped to ``0`` (and then continue to be
+overflow, the version is wrapped to ``0`` (and then continues to be
 incremented) according to the C standard.
 
 After an integer overflow, a guard can succeed whereas the watched
@@ -337,7 +338,7 @@ structure, the field has the C type ``PY_UINT64_T``. When a key is
 created or modified, the entry version is set to the dictionary version
 which is incremented at any change (create, modify, delete).
 
-Pseudo-code of an fast guard to check if a dictionary key was modified
+Pseudo-code of a fast guard to check if a dictionary key was modified
 using hypothetical ``dict_get_version(dict)`` and
 ``dict_get_entry_version(dict)`` functions::