diff --git a/packages/signature-v4-multi-region/src/SignatureV4MultiRegion.ts b/packages/signature-v4-multi-region/src/SignatureV4MultiRegion.ts
index 5297b5d6a311..e10dfa952774 100644
--- a/packages/signature-v4-multi-region/src/SignatureV4MultiRegion.ts
+++ b/packages/signature-v4-multi-region/src/SignatureV4MultiRegion.ts
@@ -78,49 +78,49 @@ export class SignatureV4MultiRegion implements RequestPresigner, RequestSigner {
 
   private getSigv4aSigner(): InstanceType<OptionalCrtSignerV4> | InstanceType<OptionalSigV4aSigner> {
     if (!this.sigv4aSigner) {
-      let CrtSignerV4: OptionalCrtSignerV4 | null = null;
-      let JsSigV4aSigner: OptionalSigV4aSigner | null = null;
+      const CrtSignerV4 = signatureV4CrtContainer.CrtSignerV4;
+      const JsSigV4aSigner = signatureV4aContainer.SignatureV4a;
 
-      if (signatureV4CrtContainer.CrtSignerV4) {
-        try {
-          CrtSignerV4 = signatureV4CrtContainer.CrtSignerV4;
-          if (typeof CrtSignerV4 !== "function") throw new Error();
-        } catch (e) {
-          e.message =
-            `${e.message}\n` +
-            `Please check whether you have installed the "@aws-sdk/signature-v4-crt" package explicitly. \n` +
-            `You must also register the package by calling [require("@aws-sdk/signature-v4-crt");] ` +
-            `or an ESM equivalent such as [import "@aws-sdk/signature-v4-crt";]. \n` +
-            "For more information please go to " +
-            "https://github.com/aws/aws-sdk-js-v3#functionality-requiring-aws-common-runtime-crt";
-          throw e;
+      if (this.signerOptions.runtime === "node") {
+        if (!CrtSignerV4 && !JsSigV4aSigner) {
+          throw new Error(
+            "Neither CRT nor JS SigV4a implementation is available. " +
+              "Please load either @aws-sdk/signature-v4-crt or @smithy/signature-v4a. " +
+              "For more information please go to " +
+              "https://github.com/aws/aws-sdk-js-v3#functionality-requiring-aws-common-runtime-crt"
+          );
         }
 
-        this.sigv4aSigner = new CrtSignerV4({
-          ...this.signerOptions,
-          signingAlgorithm: 1,
-        });
-      } else if (signatureV4aContainer.SignatureV4a) {
-        try {
-          JsSigV4aSigner = signatureV4aContainer.SignatureV4a;
-          if (typeof JsSigV4aSigner !== "function") throw new Error();
-        } catch (e) {
-          e.message =
-            `${e.message}\n` +
-            `Please check whether you have installed the "@smithy/signature-v4a" package explicitly. \n` +
-            `You must also register the package by calling [require("@smithy/signature-v4a");] ` +
-            `or an ESM equivalent such as [import "@smithy/signature-v4a";]. \n`;
-          throw e;
+        if (CrtSignerV4 && typeof CrtSignerV4 === "function") {
+          this.sigv4aSigner = new CrtSignerV4({
+            ...this.signerOptions,
+            signingAlgorithm: 1,
+          });
+        } else if (JsSigV4aSigner && typeof JsSigV4aSigner === "function") {
+          this.sigv4aSigner = new JsSigV4aSigner({
+            ...this.signerOptions,
+          });
+        } else {
+          throw new Error(
+            "Available SigV4a implementation is not a valid constructor. " +
+              "Please ensure you've properly imported @aws-sdk/signature-v4-crt or @smithy/signature-v4a."
+          );
+        }
+      } else {
+        if (!JsSigV4aSigner || typeof JsSigV4aSigner !== "function") {
+          throw new Error(
+            "JS SigV4a implementation is not available or not a valid constructor. " +
+              "Please check whether you have installed the @smithy/signature-v4a package explicitly. " +
+              "You must also register the package by calling [require('@smithy/signature-v4a');] " +
+              "or an ESM equivalent such as [import '@smithy/signature-v4a';]. " +
+              "For more information please go to " +
+              "https://github.com/aws/aws-sdk-js-v3#using-javascript-non-crt-implementation-of-sigv4a"
+          );
         }
 
         this.sigv4aSigner = new JsSigV4aSigner({
           ...this.signerOptions,
         });
-      } else {
-        throw new Error(
-          "Neither CRT nor JS SigV4a implementation is available. " +
-          "Please load either @aws-sdk/signature-v4-crt or @smithy/signature-v4a."
-        );
       }
     }
     return this.sigv4aSigner;