diff --git a/packages/source-fetcher/lib/etherscan.ts b/packages/source-fetcher/lib/etherscan.ts
index f2491ca4792..e037c8f0641 100644
--- a/packages/source-fetcher/lib/etherscan.ts
+++ b/packages/source-fetcher/lib/etherscan.ts
@@ -255,7 +255,13 @@ const EtherscanFetcher: FetcherConstructor = class EtherscanFetcher
   private static processJsonResult(
     result: EtherscanResult,
     jsonInput: Types.SolcInput
-  ): Types.SourceInfo {
+  ): Types.SourceInfo | null {
+    if (jsonInput.language === "SolidityAST") {
+      //I don't know whether this is actually possible on Etherscan,
+      //but there's no way we can reasonably handle it, so let's
+      //just be defensive and refuse it
+      return null;
+    }
     return {
       contractName: result.ContractName,
       sources: this.processSources(jsonInput.sources),
diff --git a/packages/source-fetcher/lib/types.ts b/packages/source-fetcher/lib/types.ts
index bf12986ac16..ae7495106c9 100644
--- a/packages/source-fetcher/lib/types.ts
+++ b/packages/source-fetcher/lib/types.ts
@@ -101,7 +101,7 @@ export interface SolcSources {
 }
 
 export interface SolcInput {
-  language: "Solidity";
+  language: "Solidity" | "Yul" | "SolidityAST";
   sources: SolcSources;
   settings: SolcSettings;
 }