diff --git a/Library/Homebrew/extend/ENV/shared.rb b/Library/Homebrew/extend/ENV/shared.rb
index 57b9a7f1ed..19af48698c 100644
--- a/Library/Homebrew/extend/ENV/shared.rb
+++ b/Library/Homebrew/extend/ENV/shared.rb
@@ -203,6 +203,12 @@ module SharedEnvExtension
   end
 
   def fortran
+    # Ignore repeated calls to this function as it will misleadingly warn about
+    # building with an alternative Fortran compiler without optimization flags,
+    # despite it often being the Homebrew-provided one set up in the first call.
+    return if @fortran_setup_done
+    @fortran_setup_done = true
+
     flags = []
 
     if fc