diff --git a/key_test.go b/key_test.go
index 1bbaf10..3f064df 100644
--- a/key_test.go
+++ b/key_test.go
@@ -77,7 +77,7 @@ func TestMarshal(t *testing.T) {
 	}
 	tls_der := x509.MarshalPKCS1PrivateKey(tls_key)
 	if !bytes.Equal(der, tls_der) {
-		t.Fatal("invalid private key der bytes: %s\n v.s. %s\n",
+		t.Fatalf("invalid private key der bytes: %s\n v.s. %s\n",
 			hex.Dump(der), hex.Dump(tls_der))
 	}
 
@@ -291,7 +291,7 @@ func TestMarshalEC(t *testing.T) {
 		t.Fatal(err)
 	}
 	if !bytes.Equal(der, tls_der) {
-		t.Fatal("invalid private key der bytes: %s\n v.s. %s\n",
+		t.Fatalf("invalid private key der bytes: %s\n v.s. %s\n",
 			hex.Dump(der), hex.Dump(tls_der))
 	}
 
diff --git a/sha1_test.go b/sha1_test.go
index 2c25978..37808b5 100644
--- a/sha1_test.go
+++ b/sha1_test.go
@@ -35,7 +35,7 @@ func TestSHA1(t *testing.T) {
 		}
 
 		if expected != got {
-			t.Fatal("exp:%x got:%x", expected, got)
+			t.Fatalf("exp:%x got:%x", expected, got)
 		}
 	}
 }
@@ -73,7 +73,7 @@ func TestSHA1Writer(t *testing.T) {
 		}
 
 		if got != exp {
-			t.Fatal("exp:%x got:%x", exp, got)
+			t.Fatalf("exp:%x got:%x", exp, got)
 		}
 	}
 }
diff --git a/sha256_test.go b/sha256_test.go
index b4e7af8..467e503 100644
--- a/sha256_test.go
+++ b/sha256_test.go
@@ -35,7 +35,7 @@ func TestSHA256(t *testing.T) {
 		}
 
 		if expected != got {
-			t.Fatal("exp:%x got:%x", expected, got)
+			t.Fatalf("exp:%x got:%x", expected, got)
 		}
 	}
 }
@@ -73,7 +73,7 @@ func TestSHA256Writer(t *testing.T) {
 		}
 
 		if got != exp {
-			t.Fatal("exp:%x got:%x", exp, got)
+			t.Fatalf("exp:%x got:%x", exp, got)
 		}
 	}
 }