diff --git a/src/signature.rs b/src/signature.rs
index ea96ebc..481947c 100644
--- a/src/signature.rs
+++ b/src/signature.rs
@@ -71,7 +71,9 @@ impl Signature {
 				hasher.update(&header);
 			}
 		}
-		hasher.update(self.get_header().as_bytes());
+		let dkim_header = self.get_header();
+		let dkim_header = self.canonicalization.process_header(dkim_header.as_bytes());
+		hasher.update(dkim_header);
 		hasher.finalize().to_vec()
 	}
 }