diff --git a/packages/sdk/src/cosmwasmclient.ts b/packages/sdk/src/cosmwasmclient.ts
index 126e3b69..370ce332 100644
--- a/packages/sdk/src/cosmwasmclient.ts
+++ b/packages/sdk/src/cosmwasmclient.ts
@@ -114,6 +114,7 @@ export interface IndexedTx {
   readonly gasWanted?: number;
   /** The gas used by the execution */
   readonly gasUsed?: number;
+  /** An RFC 3339 time string like e.g. '2020-02-15T10:39:10.4696305Z' */
   readonly timestamp: string;
 }
 
diff --git a/packages/sdk/types/cosmwasmclient.d.ts b/packages/sdk/types/cosmwasmclient.d.ts
index 4b92801b..83afe61f 100644
--- a/packages/sdk/types/cosmwasmclient.d.ts
+++ b/packages/sdk/types/cosmwasmclient.d.ts
@@ -83,6 +83,7 @@ export interface IndexedTx {
   readonly gasWanted?: number;
   /** The gas used by the execution */
   readonly gasUsed?: number;
+  /** An RFC 3339 time string like e.g. '2020-02-15T10:39:10.4696305Z' */
   readonly timestamp: string;
 }
 export interface BlockHeader {