diff --git a/Fortran/UnitTests/fcvs21_f95/CMakeLists.txt b/Fortran/UnitTests/fcvs21_f95/CMakeLists.txt
--- a/Fortran/UnitTests/fcvs21_f95/CMakeLists.txt
+++ b/Fortran/UnitTests/fcvs21_f95/CMakeLists.txt
@@ -33,13 +33,19 @@
 # clean-up fort.* files otherwise one of the tests will fail
 llvm_test_prepare(rm -f %S/fort.*)
 
-# Test 509 requires this flag in more recent versions of GCC
+file(GLOB Source CONFIGURE_DEPENDS *.f)
+
+# Test 509 requires this flag in more recent versions of GCC.
+# If this flag is not supported, the test should be excluded.
 check_fortran_compiler_flag("-std=legacy" SUPPORTS_LEGACY)
 if (SUPPORTS_LEGACY)
   add_compile_options(-std=legacy)
-endif ()
+else()
+  # Regex because the GLOB returns the full path to each file
+  list(FILTER Source EXCLUDE REGEX "FM509\.f$")
+endif()
 
 set(FP_TOLERANCE 1.0e-11) # set by the most sensitive numerical test
-llvm_singlesource()
+llvm_singlesource(${Source})
 
 file(COPY lit.local.cfg DESTINATION "${CMAKE_CURRENT_BINARY_DIR}")
diff --git a/cmake/modules/SingleMultiSource.cmake b/cmake/modules/SingleMultiSource.cmake
--- a/cmake/modules/SingleMultiSource.cmake
+++ b/cmake/modules/SingleMultiSource.cmake
@@ -7,16 +7,16 @@
 #
 # Defines helpers to add executables and tests. The entry points to this
 # file are:
-#   `llvm_singlesource([PREFIX p])`, and
+#   `llvm_singlesource([PREFIX p] [sources...])`, and
 #   `llvm_multisource()`
 #
 # Following convenience functions provide shortcuts for common test cases:
 #
-# llvm_singlesource([PREFIX p])
+# llvm_singlesource([PREFIX p] [sources...])
 #
-#   Invokes llvm_test_executable() for each c/c++ source file.  If
-#   'sources is emptyno sources are specified, creates test executables
-#   for all C/C++ files in current directory.
+#   Invokes llvm_test_executable() for each C/C++/Fortran source file.
+#   If sources is empty, creates test executables for all C/C++/Fortran
+#   files in current directory.
 #   Passes optional PREFIX parameter to llvm_test_executable().
 #
 # llvm_multisource(target)
@@ -27,14 +27,22 @@
 include(TestSuite)
 
 # Configure the current directory as a SingleSource subdirectory - i.e. every
-# file in *.{c,cpp,cc} is treated as its own test.
+# C/C++/Fortran file is treated as its own test.
 function(llvm_singlesource)
+  # PREFIX is optional so it cannot be a named argument.
   cmake_parse_arguments(_LSARG "" "PREFIX" "" ${ARGN})
-  if(DEFINED Source)
-    set(sources ${Source})
-  else()
+  if(DEFINED _LSARG_PREFIX)
+    # Remove "PREFIX" and the associated value from ARGN so that it only
+    # contains sources.
+    list(REMOVE_AT ARGN 0)
+    list(REMOVE_AT ARGN 0)
+  endif()
+
+  set(sources ${ARGN})
+  if(NOT sources)
     file(GLOB sources *.c *.cpp *.cc *.f *.F *.f90 *.F90)
   endif()
+
   foreach(source ${sources})
     basename(name ${source})
     set(_target ${_LSARG_PREFIX}${name})