diff --git a/flang/tools/f18/f18.cpp b/flang/tools/f18/f18.cpp
--- a/flang/tools/f18/f18.cpp
+++ b/flang/tools/f18/f18.cpp
@@ -639,21 +639,26 @@
   if (driver.warnOnNonstandardUsage) {
     options.features.WarnOnAllNonstandard();
   }
-  if (options.features.IsEnabled(Fortran::common::LanguageFeature::OpenMP)) {
-    driver.pgf90Args.push_back("-mp");
-  }
   if (isPGF90) {
     if (!options.features.IsEnabled(
             Fortran::common::LanguageFeature::BackslashEscapes)) {
       driver.pgf90Args.push_back(
           "-Mbackslash"); // yes, this *disables* them in pgf90
     }
+    if (options.features.IsEnabled(Fortran::common::LanguageFeature::OpenMP)) {
+      driver.pgf90Args.push_back("-mp");
+    }
+
     Fortran::parser::useHexadecimalEscapeSequences = false;
   } else {
     if (options.features.IsEnabled(
             Fortran::common::LanguageFeature::BackslashEscapes)) {
       driver.pgf90Args.push_back("-fbackslash");
     }
+    if (options.features.IsEnabled(Fortran::common::LanguageFeature::OpenMP)) {
+      driver.pgf90Args.push_back("-fopenmp");
+    }
+
     Fortran::parser::useHexadecimalEscapeSequences = true;
   }