diff --git a/ppc64/ppc64asm/ext_test.go b/ppc64/ppc64asm/ext_test.go
index 01abefb..b553984 100644
--- a/ppc64/ppc64asm/ext_test.go
+++ b/ppc64/ppc64asm/ext_test.go
@@ -176,7 +176,7 @@
 	t.Logf("%d test cases, %d expected mismatches, %d failures; %.0f cases/second", totalTests, totalSkips, totalErrors, float64(totalTests)/time.Since(start).Seconds())
 
 	if err := <-errc; err != nil {
-		t.Fatal("external disassembler: %v", err)
+		t.Fatalf("external disassembler: %v", err)
 	}
 
 }
diff --git a/ppc64/ppc64asm/inst.go b/ppc64/ppc64asm/inst.go
index bf72ac6..89481ca 100644
--- a/ppc64/ppc64asm/inst.go
+++ b/ppc64/ppc64asm/inst.go
@@ -200,7 +200,7 @@
 	case V0 <= r && r <= V63:
 		return fmt.Sprintf("v%d", int(r-V0))
 	default:
-		return fmt.Sprint("Reg(%d)", int(r))
+		return fmt.Sprintf("Reg(%d)", int(r))
 	}
 }