diff --git a/flang/lib/Frontend/FrontendOptions.cpp b/flang/lib/Frontend/FrontendOptions.cpp
--- a/flang/lib/Frontend/FrontendOptions.cpp
+++ b/flang/lib/Frontend/FrontendOptions.cpp
@@ -13,17 +13,17 @@
 
 bool Fortran::frontend::isFixedFormSuffix(llvm::StringRef suffix) {
   // Note: Keep this list in-sync with flang/test/lit.cfg.py
-  return suffix == "f" || suffix == "F" || suffix == "ff" || suffix == "for" ||
-      suffix == "FOR" || suffix == "fpp" || suffix == "FPP";
+  return suffix == "f77" || suffix == "f" || suffix == "F" || suffix == "ff" ||
+      suffix == "for" || suffix == "FOR" || suffix == "fpp" || suffix == "FPP";
 }
 
 bool Fortran::frontend::isFreeFormSuffix(llvm::StringRef suffix) {
   // Note: Keep this list in-sync with flang/test/lit.cfg.py
   // TODO: Add Cuda Fortan files (i.e. `*.cuf` and `*.CUF`).
-  return suffix == "f77" || suffix == "f90" || suffix == "F90" ||
-      suffix == "ff90" || suffix == "f95" || suffix == "F95" ||
-      suffix == "ff95" || suffix == "f03" || suffix == "F03" ||
-      suffix == "f08" || suffix == "F08" || suffix == "f18" || suffix == "F18";
+  return suffix == "f90" || suffix == "F90" || suffix == "ff90" ||
+      suffix == "f95" || suffix == "F95" || suffix == "ff95" ||
+      suffix == "f03" || suffix == "F03" || suffix == "f08" ||
+      suffix == "F08" || suffix == "f18" || suffix == "F18";
 }
 
 // TODO: This is a copy of `asFortran` from f18.cpp and is added here for