diff --git a/src/Environment.cc b/src/Environment.cc
index 73c996c..63e0746 100644
--- a/src/Environment.cc
+++ b/src/Environment.cc
@@ -18,8 +18,7 @@
 #include <gz/utils/Environment.hh>
 
 #include <cstdlib>
-#include <iostream>
-
+#include <string>
 
 namespace gz
 {
diff --git a/src/Environment_TEST.cc b/src/Environment_TEST.cc
index 7968577..8168153 100644
--- a/src/Environment_TEST.cc
+++ b/src/Environment_TEST.cc
@@ -19,6 +19,8 @@
 
 #include <gz/utils/Environment.hh>
 
+#include <string>
+
 using namespace gz;
 
 /////////////////////////////////////////////////
diff --git a/src/NeverDestroyed_TEST.cc b/src/NeverDestroyed_TEST.cc
index 30d2b73..1b670b8 100644
--- a/src/NeverDestroyed_TEST.cc
+++ b/src/NeverDestroyed_TEST.cc
@@ -19,7 +19,12 @@
 
 #include <gtest/gtest.h>
 
+#include <cstdint>
+#include <exception>
+#include <initializer_list>
 #include <random>
+#include <string>
+#include <vector>
 #include <unordered_map>
 
 using namespace gz;
diff --git a/test/integration/implptr/ImplPtr_TEST.cc b/test/integration/implptr/ImplPtr_TEST.cc
index 3154421..eedbdb9 100644
--- a/test/integration/implptr/ImplPtr_TEST.cc
+++ b/test/integration/implptr/ImplPtr_TEST.cc
@@ -17,9 +17,10 @@
 
 #include <gtest/gtest.h>
 
-#include <gz/utils/ImplPtr.hh>
 #include "implptr_test_classes.hh"
 
+#include <utility>
+
 using namespace gz::implptr_test_classes;
 
 /////////////////////////////////////////////////
diff --git a/test/integration/implptr/implptr_test_classes.cc b/test/integration/implptr/implptr_test_classes.cc
index 1d13a78..0603bb2 100644
--- a/test/integration/implptr/implptr_test_classes.cc
+++ b/test/integration/implptr/implptr_test_classes.cc
@@ -17,6 +17,8 @@
 
 #include "implptr_test_classes.hh"
 
+#include <gz/utils/ImplPtr.hh>
+
 #include <string>
 #include <thread>
 
@@ -153,4 +155,3 @@ void CopyableObjectAlt::SetString(const std::string &_value)
 {
   (*dataPtr).svalue = _value;
 }
-
diff --git a/test/integration/implptr/implptr_test_classes.hh b/test/integration/implptr/implptr_test_classes.hh
index 5b5f2a0..b9e5b3b 100644
--- a/test/integration/implptr/implptr_test_classes.hh
+++ b/test/integration/implptr/implptr_test_classes.hh
@@ -42,7 +42,7 @@ namespace gz
       public: int GetInt() const;
 
       /// \brief Set the int value held by the pimpl
-      public: void SetInt(const int _value);
+      public: void SetInt(int _value);
 
       /// \brief Get the string value held by the pimpl
       public: const std::string &GetString() const;
@@ -72,7 +72,7 @@ namespace gz
       public: int GetInt() const;
 
       /// \brief Set the int value held by the pimpl
-      public: void SetInt(const int _value);
+      public: void SetInt(int _value);
 
       /// \brief Get the string value held by the pimpl
       public: const std::string &GetString() const;
@@ -102,7 +102,7 @@ namespace gz
       public: int GetInt() const;
 
       /// \brief Set the int value held by the pimpl
-      public: void SetInt(const int _value);
+      public: void SetInt(int _value);
 
       /// \brief Get the string value held by the pimpl
       public: const std::string &GetString() const;