diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
index b8874430d30..ae3a137e87f 100644
--- a/accel/tcg/tcg-all.c
+++ b/accel/tcg/tcg-all.c
@@ -32,6 +32,7 @@
 #include "qemu/error-report.h"
 #include "qemu/accel.h"
 #include "qemu/atomic.h"
+#include "qapi/qapi-types-common.h"
 #include "qapi/qapi-builtin-visit.h"
 #include "qemu/units.h"
 #if defined(CONFIG_USER_ONLY)
@@ -47,7 +48,7 @@
 struct TCGState {
     AccelState parent_obj;
 
-    bool mttcg_enabled;
+    OnOffAuto mttcg_enabled;
     bool one_insn_per_tb;
     int splitwx_enabled;
     unsigned long tb_size;
@@ -70,37 +71,10 @@ bool qemu_tcg_mttcg_enabled(void)
 
 #endif /* !CONFIG_USER_ONLY */
 
-/*
- * We default to false if we know other options have been enabled
- * which are currently incompatible with MTTCG. Otherwise when each
- * guest (target) has been updated to support:
- *   - atomic instructions
- *   - memory ordering primitives (barriers)
- * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
- *
- * Once a guest architecture has been converted to the new primitives
- * there is one remaining limitation to check:
- *   - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
- */
-
-static bool default_mttcg_enabled(void)
-{
-    if (icount_enabled()) {
-        return false;
-    }
-#ifdef TARGET_SUPPORTS_MTTCG
-    return true;
-#else
-    return false;
-#endif
-}
-
 static void tcg_accel_instance_init(Object *obj)
 {
     TCGState *s = TCG_STATE(obj);
 
-    s->mttcg_enabled = default_mttcg_enabled();
-
     /* If debugging enabled, default "auto on", otherwise off. */
 #if defined(CONFIG_DEBUG_TCG) && !defined(CONFIG_USER_ONLY)
     s->splitwx_enabled = -1;
@@ -118,7 +92,35 @@ static int tcg_init_machine(MachineState *ms)
     unsigned max_cpus = 1;
 #else
     unsigned max_cpus = ms->smp.max_cpus;
+#ifdef TARGET_SUPPORTS_MTTCG
+    bool mttcg_supported = true;
+#else
+    bool mttcg_supported = false;
+#endif
 
+    if (s->mttcg_enabled == ON_OFF_AUTO_AUTO) {
+        /*
+         * We default to false if we know other options have been enabled
+         * which are currently incompatible with MTTCG. Otherwise when each
+         * guest (target) has been updated to support:
+         *   - atomic instructions
+         *   - memory ordering primitives (barriers)
+         * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
+         *
+         * Once a guest architecture has been converted to the new primitives
+         * there is one remaining limitation to check:
+         *   - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
+         */
+        if (icount_enabled()) {
+            s->mttcg_enabled = ON_OFF_AUTO_OFF;
+        } else {
+            s->mttcg_enabled = mttcg_supported;
+        }
+    }
+    if (s->mttcg_enabled == ON_OFF_AUTO_ON && !mttcg_supported) {
+        warn_report("Guest not yet converted to MTTCG - "
+                    "you may get unexpected results");
+    }
     mttcg_enabled = s->mttcg_enabled;
 #endif
 
@@ -147,7 +149,7 @@ static char *tcg_get_thread(Object *obj, Error **errp)
 {
     TCGState *s = TCG_STATE(obj);
 
-    return g_strdup(s->mttcg_enabled ? "multi" : "single");
+    return g_strdup(s->mttcg_enabled == ON_OFF_AUTO_ON ? "multi" : "single");
 }
 
 static void tcg_set_thread(Object *obj, const char *value, Error **errp)
@@ -158,14 +160,10 @@ static void tcg_set_thread(Object *obj, const char *value, Error **errp)
         if (icount_enabled()) {
             error_setg(errp, "No MTTCG when icount is enabled");
         } else {
-#ifndef TARGET_SUPPORTS_MTTCG
-            warn_report("Guest not yet converted to MTTCG - "
-                        "you may get unexpected results");
-#endif
-            s->mttcg_enabled = true;
+            s->mttcg_enabled = ON_OFF_AUTO_ON;
         }
     } else if (strcmp(value, "single") == 0) {
-        s->mttcg_enabled = false;
+        s->mttcg_enabled = ON_OFF_AUTO_OFF;
     } else {
         error_setg(errp, "Invalid 'thread' setting %s", value);
     }
