diff --git a/dist/index.js b/dist/index.js
index fa1564be..7b763e8d 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -580,6 +580,9 @@ function run() {
             if (!originalArchInput) { // if `originalArchInput` is an empty string
                 throw new Error(`Arch input must not be null`);
             }
+            if (originalArchInput == 'x64' && os.platform() == 'darwin' && os.arch() == 'arm64') {
+                core.warning('[setup-julia] x64 arch has been requested on a macOS runner that has an arm64 architecture. You may have meant to use the "aarch64" arch instead (or left it unspecified for the correct default).');
+            }
             let processedArchInput;
             if (originalArchInput == "default") {
                 // If the user sets the `arch` input to `default`, then we use the
diff --git a/lib/setup-julia.js b/lib/setup-julia.js
index 471adfd0..087b0f2d 100644
--- a/lib/setup-julia.js
+++ b/lib/setup-julia.js
@@ -88,6 +88,9 @@ function run() {
             if (!originalArchInput) { // if `originalArchInput` is an empty string
                 throw new Error(`Arch input must not be null`);
             }
+            if (originalArchInput == 'x64' && os.platform() == 'darwin' && os.arch() == 'arm64') {
+                core.warning('[setup-julia] x64 arch has been requested on a macOS runner that has an arm64 architecture. You may have meant to use the "aarch64" arch instead (or left it unspecified for the correct default).');
+            }
             let processedArchInput;
             if (originalArchInput == "default") {
                 // If the user sets the `arch` input to `default`, then we use the
diff --git a/src/setup-julia.ts b/src/setup-julia.ts
index 9ff3990a..8ea8c621 100644
--- a/src/setup-julia.ts
+++ b/src/setup-julia.ts
@@ -62,6 +62,10 @@ async function run() {
             throw new Error(`Arch input must not be null`)
         }
 
+        if (originalArchInput == 'x64' && os.platform() == 'darwin' && os.arch() == 'arm64') {
+            core.warning('[setup-julia] x64 arch has been requested on a macOS runner that has an arm64 architecture. You may have meant to use the "aarch64" arch instead (or left it unspecified for the correct default).')
+        }
+
         let processedArchInput: string;
         if (originalArchInput == "default") {
             // If the user sets the `arch` input to `default`, then we use the