diff --git a/doc/src/Developer_platform.rst b/doc/src/Developer_platform.rst
index 4cea36f94c..fd5cf065eb 100644
--- a/doc/src/Developer_platform.rst
+++ b/doc/src/Developer_platform.rst
@@ -115,6 +115,9 @@ Environment variable functions
 .. doxygenfunction:: putenv
    :project: progguide
 
+.. doxygenfunction:: unsetenv
+   :project: progguide
+
 .. doxygenfunction:: list_pathenv
    :project: progguide
 
diff --git a/src/platform.cpp b/src/platform.cpp
index 555026b2ac..5e04251ca7 100644
--- a/src/platform.cpp
+++ b/src/platform.cpp
@@ -442,6 +442,27 @@ int platform::putenv(const std::string &vardef)
   return -1;
 }
 
+/* ----------------------------------------------------------------------
+   unset environment variable
+------------------------------------------------------------------------- */
+
+int platform::unsetenv(const std::string &variable)
+{
+  if (variable.size() == 0) return -1;
+
+#ifdef _WIN32
+  // empty _putenv() definition deletes variable on Windows
+  // must not have an equal sign as that will result in creating an environment variable
+  if (variable.find_first_of('=') != std::string::npos) return -1;
+  auto var = utils::strdup(variable);
+  int rv = _putenv(var);
+  delete[] var;
+  return rv;
+#else
+  return ::unsetenv(variable.c_str());
+#endif
+}
+
 /* ----------------------------------------------------------------------
    split a "path" environment variable into a list
 ------------------------------------------------------------------------- */
diff --git a/src/platform.h b/src/platform.h
index de8ecce016..eb14b403aa 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -116,6 +116,13 @@ namespace platform {
 
   int putenv(const std::string &vardef);
 
+  /*! Delete variable from the environment
+   *
+   * \param  variable  variable name
+   * \return -1 if failure otherwise 0 */
+
+  int unsetenv(const std::string &variable);
+
   /*! Get list of entries in a path environment variable
    *
    * This provides a list of strings of the entries in an environment
diff --git a/unittest/cplusplus/test_lammps_class.cpp b/unittest/cplusplus/test_lammps_class.cpp
index 663c7358d9..3a1bde51ff 100644
--- a/unittest/cplusplus/test_lammps_class.cpp
+++ b/unittest/cplusplus/test_lammps_class.cpp
@@ -363,11 +363,7 @@ TEST(LAMMPS_init, NoOpenMP)
     FILE *fp = fopen("in.lammps_class_noomp", "w");
     fputs("\n", fp);
     fclose(fp);
-#if defined(__WIN32)
-    _putenv("OMP_NUM_THREADS");
-#else
-    unsetenv("OMP_NUM_THREADS");
-#endif
+    platform::unsetenv("OMP_NUM_THREADS");
 
     const char *args[] = {"LAMMPS_init", "-in", "in.lammps_class_noomp", "-log", "none", "-nocite"};
     char **argv        = (char **)args;
diff --git a/unittest/utils/test_platform.cpp b/unittest/utils/test_platform.cpp
index 0f39534c31..ace546ba90 100644
--- a/unittest/utils/test_platform.cpp
+++ b/unittest/utils/test_platform.cpp
@@ -37,7 +37,7 @@ TEST(Platform, clock)
     ASSERT_GT(ct_used, 1e-4);
 }
 
-TEST(Platform, putenv)
+TEST(Platform, putenv_unsetenv)
 {
     const char *var = getenv("UNITTEST_VAR1");
     ASSERT_EQ(var, nullptr);
@@ -65,6 +65,14 @@ TEST(Platform, putenv)
     ASSERT_THAT(var, StrEq("one=two"));
 
     ASSERT_EQ(platform::putenv(""), -1);
+
+    ASSERT_EQ(platform::unsetenv(""), -1);
+    ASSERT_EQ(platform::unsetenv("UNITTEST_VAR3=two"), -1);
+    var    = getenv("UNITTEST_VAR1");
+    ASSERT_NE(var, nullptr);
+    ASSERT_EQ(platform::unsetenv("UNITTEST_VAR1"), 0);
+    var    = getenv("UNITTEST_VAR1");
+    ASSERT_EQ(var, nullptr);
 }
 
 TEST(Platform, list_pathenv)