diff --git a/Library/Homebrew/extend/os/mac/hardware/cpu.rb b/Library/Homebrew/extend/os/mac/hardware/cpu.rb
index 03269d48fd..919c47bc84 100644
--- a/Library/Homebrew/extend/os/mac/hardware/cpu.rb
+++ b/Library/Homebrew/extend/os/mac/hardware/cpu.rb
@@ -63,6 +63,14 @@ module Hardware
         [arch_64_bit, arch_32_bit].extend ArchitectureListExtension
       end
 
+      # True when running under an Intel-based shell via Rosetta on an
+      # Apple Silicon Mac. This can be detected via seeing if there's a
+      # conflict between what `uname` report and the underlying `sysctl` flags,
+      # since the `sysctl` flags don't change behaviour under Rosetta.
+      def running_under_rosetta?
+        intel? && physical_cpu_arm64?
+      end
+
       def features
         @features ||= sysctl_n(
           "machdep.cpu.features",
@@ -109,6 +117,12 @@ module Hardware
 
       private
 
+      # Note: this is more reliable than checking uname.
+      # `sysctl` returns the right answer even when running in Rosetta.
+      def physical_cpu_arm64?
+        sysctl_bool("hw.optional.arm64")
+      end
+
       def sysctl_bool(key)
         sysctl_int(key) == 1
       end
diff --git a/Library/Homebrew/hardware.rb b/Library/Homebrew/hardware.rb
index 5d93e7df92..4d02fef9aa 100644
--- a/Library/Homebrew/hardware.rb
+++ b/Library/Homebrew/hardware.rb
@@ -154,6 +154,10 @@ module Hardware
 
         "-march=#{arch}"
       end
+
+      def running_under_rosetta?
+        false
+      end
     end
   end