diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 235f5cab674..2e7005d912e 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -3875,7 +3875,7 @@ namespace ts {
     }
 
     export interface Signature {
-        declaration: SignatureDeclaration;  // Originating declaration
+        declaration?: SignatureDeclaration; // Originating declaration
         typeParameters?: TypeParameter[];   // Type parameters (undefined if non-generic)
         parameters: Symbol[];               // Parameters
         /* @internal */
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index 2b8bf0d2a40..8b9e078716c 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -2223,7 +2223,7 @@ declare namespace ts {
         Construct = 1,
     }
     interface Signature {
-        declaration: SignatureDeclaration;
+        declaration?: SignatureDeclaration;
         typeParameters?: TypeParameter[];
         parameters: Symbol[];
     }
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index d77850c0c52..87204f489d8 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -2223,7 +2223,7 @@ declare namespace ts {
         Construct = 1,
     }
     interface Signature {
-        declaration: SignatureDeclaration;
+        declaration?: SignatureDeclaration;
         typeParameters?: TypeParameter[];
         parameters: Symbol[];
     }