diff --git a/run_tests.py b/run_tests.py
index 59e5930..2c3f927 100644
--- a/run_tests.py
+++ b/run_tests.py
@@ -8,7 +8,7 @@ import subprocess as sp
 COMPILER = getenv("CXX", "c++")
 CXXFLAGS = [
     "-std=c++14",
-    "-Wall", "-Wextra",
+    "-Wall", "-Wextra", "-Wshadow",
     "-Wno-missing-braces", # clang false positive
     "-I."
 ] + getenv("CXXFLAGS", "").split()
diff --git a/tests/utility.cc b/tests/utility.cc
index 44bd63b..d4d0c35 100644
--- a/tests/utility.cc
+++ b/tests/utility.cc
@@ -7,24 +7,24 @@ using namespace ostd;
 struct Foo {
     int x;
     Foo(): x(5) {}
-    Foo(int x): x(x) {}
-    Foo(const Foo &x): x(x.x) {}
-    Foo(Foo &&x): x(x.x) { x.x = 0; }
-    Foo &operator=(int _x) {
-        x = _x;
+    Foo(int v): x(v) {}
+    Foo(const Foo &o): x(o.x) {}
+    Foo(Foo &&o): x(o.x) { o.x = 0; }
+    Foo &operator=(int v) {
+        x = v;
         return *this;
     }
 };
 
 struct NotSwappable {
     int i;
-    NotSwappable(int i): i(i) {}
+    NotSwappable(int v): i(v) {}
 };
 
 struct Swappable {
     int i;
     bool swapped;
-    Swappable(int i): i(i), swapped(false) {}
+    Swappable(int v): i(v), swapped(false) {}
     void swap(Swappable &v) {
         auto j = i;
         i = v.i;