diff --git a/src/x87.c b/src/x87.c
index 44f22e0..ac2650d 100644
--- a/src/x87.c
+++ b/src/x87.c
@@ -35,7 +35,7 @@ uint16_t x87_gettag()
                         ret |= X87_TAG_EMPTY << (c * 2);
                 else if (cpu_state.tag[c] & TAG_UINT64)
                         ret |= 2 << (c*2);
-                else if (cpu_state.ST[c] == 0.0)
+                else if (cpu_state.ST[c] == 0.0 && !cpu_state.ismmx)
                         ret |= X87_TAG_ZERO << (c * 2);
                 else
                         ret |= X87_TAG_VALID << (c * 2);
diff --git a/src/x87.h b/src/x87.h
index 2ec4405..9441a41 100644
--- a/src/x87.h
+++ b/src/x87.h
@@ -9,7 +9,7 @@ uint16_t x87_pc_seg,x87_op_seg;
 static inline void x87_set_mmx()
 {
         cpu_state.TOP = 0;
-        *(uint64_t *)cpu_state.tag = 0;
+        *(uint64_t *)cpu_state.tag = 0x0101010101010101ull;
         cpu_state.ismmx = 1;
 }
 
diff --git a/src/x87_ops_misc.h b/src/x87_ops_misc.h
index f22d618..0cae387 100644
--- a/src/x87_ops_misc.h
+++ b/src/x87_ops_misc.h
@@ -117,8 +117,8 @@ static int FSTOR()
           something like this is needed*/
         if (cpu_state.MM_w4[0] == 0xffff && cpu_state.MM_w4[1] == 0xffff && cpu_state.MM_w4[2] == 0xffff && cpu_state.MM_w4[3] == 0xffff &&
             cpu_state.MM_w4[4] == 0xffff && cpu_state.MM_w4[5] == 0xffff && cpu_state.MM_w4[6] == 0xffff && cpu_state.MM_w4[7] == 0xffff &&
-            !cpu_state.TOP && !(*(uint64_t *)cpu_state.tag))
-        cpu_state.ismmx = 1;
+            !cpu_state.TOP && (*(uint64_t *)cpu_state.tag == 0x0101010101010101ull))
+                cpu_state.ismmx = 1;
 
         CLOCK_CYCLES((cr0 & 1) ? 34 : 44);
         if (fplog) pclog("FRSTOR %08X:%08X %i %i %04X\n", easeg, cpu_state.eaaddr, cpu_state.ismmx, cpu_state.TOP, x87_gettag());