diff --git a/src/arch/x86/isa/formats/monitor_mwait.isa b/src/arch/x86/isa/formats/monitor_mwait.isa
index 493b7c58a3..b26c1f2670 100644
--- a/src/arch/x86/isa/formats/monitor_mwait.isa
+++ b/src/arch/x86/isa/formats/monitor_mwait.isa
@@ -112,9 +112,9 @@ output decoder {{
     {
         std::stringstream response;
 
+        // Although mwait could take hints from eax and ecx, the _srcRegIdx
+        // is not set, and thus should not be printed here
         printMnemonic(response, mnemonic);
-        ccprintf(response, " ");
-        printReg(response, _srcRegIdx[0], machInst.opSize);
         return response.str();
     }
 }};