diff --git a/src/asmjit/x86/x86instdb.cpp b/src/asmjit/x86/x86instdb.cpp
index e869bfd..88a6976 100644
--- a/src/asmjit/x86/x86instdb.cpp
+++ b/src/asmjit/x86/x86instdb.cpp
@@ -2997,11 +2997,11 @@ const InstDB::InstSignature InstDB::_instSignatureTable[] = {
   ROW(3, 1, 1, 1, 27 , 4  , 33 , 0  , 0  , 0  ), //      {r16|m16|mem, r16, <ax>}
   ROW(3, 1, 1, 1, 28 , 6  , 36 , 0  , 0  , 0  ), //      {r32|m32|mem, r32, <eax>}
   ROW(3, 0, 1, 1, 15 , 8  , 38 , 0  , 0  , 0  ), //      {r64|m64|mem, r64, <rax>}
-  ROW(1, 1, 1, 0, 69 , 0  , 0  , 0  , 0  , 0  ), // #127 {r16|m16|r64|m64|mem}
+  ROW(1, 1, 1, 0, 69 , 0  , 0  , 0  , 0  , 0  ), // #127 {r16|m16|r64|m64}
   ROW(1, 1, 0, 0, 13 , 0  , 0  , 0  , 0  , 0  ), //      {r32|m32}
   ROW(1, 1, 0, 0, 70 , 0  , 0  , 0  , 0  , 0  ), //      {ds|es|ss}
   ROW(1, 1, 1, 0, 71 , 0  , 0  , 0  , 0  , 0  ), //      {fs|gs}
-  ROW(1, 1, 1, 0, 72 , 0  , 0  , 0  , 0  , 0  ), // #131 {r16|m16|r64|m64|mem|i8|i16|i32}
+  ROW(1, 1, 1, 0, 72 , 0  , 0  , 0  , 0  , 0  ), // #131 {r16|m16|r64|m64|i8|i16|i32}
   ROW(1, 1, 0, 0, 73 , 0  , 0  , 0  , 0  , 0  ), //      {r32|m32|i32|u32}
   ROW(1, 1, 0, 0, 74 , 0  , 0  , 0  , 0  , 0  ), //      {cs|ss|ds|es}
   ROW(1, 1, 1, 0, 71 , 0  , 0  , 0  , 0  , 0  ), //      {fs|gs}
@@ -3424,10 +3424,10 @@ const InstDB::OpSignature InstDB::_opSignatureTable[] = {
   ROW(F(Vm), M(Vm64y), 0, 0x00),
   ROW(F(Vm), M(Vm64z), 0, 0x00),
   ROW(F(GpbLo) | F(Implicit), 0, 0, 0x01),
-  ROW(F(Gpw) | F(Gpq) | F(Mem), M(M16) | M(M64) | M(Any), 0, 0x00),
+  ROW(F(Gpw) | F(Gpq) | F(Mem), M(M16) | M(M64), 0, 0x00),
   ROW(F(SReg), 0, 0, 0x1A),
   ROW(F(SReg), 0, 0, 0x60),
-  ROW(F(Gpw) | F(Gpq) | F(Mem) | F(I8) | F(I16) | F(I32), M(M16) | M(M64) | M(Any), 0, 0x00),
+  ROW(F(Gpw) | F(Gpq) | F(Mem) | F(I8) | F(I16) | F(I32), M(M16) | M(M64), 0, 0x00),
   ROW(F(Gpd) | F(Mem) | F(I32) | F(U32), M(M32), 0, 0x00),
   ROW(F(SReg), 0, 0, 0x1E),
   ROW(F(Vm), M(Vm64x) | M(Vm64y), 0, 0x00),
diff --git a/tools/tablegen-x86.js b/tools/tablegen-x86.js
index 9bb1b9d..2d6f7a0 100644
--- a/tools/tablegen-x86.js
+++ b/tools/tablegen-x86.js
@@ -282,6 +282,20 @@ class GenUtils {
     }
   }
 
+  // Prevent some instructions from having implicit memory size if that would
+  // make them ambiguous. There are some instructions where the ambiguity is
+  // okay, but some like 'push' and 'pop' where it isn't.
+  static canUseImplicitMemSize(name) {
+    switch (name) {
+      case "pop":
+      case "push":
+        return false;
+
+      default:
+        return true;
+    }
+  }
+
   static singleRegCase(name) {
     switch (name) {
       case "xchg"    :
@@ -1406,7 +1420,8 @@ class SignatureArray extends Array {
       // Patch all instructions to accept implicit-size memory operand.
       for (bIndex = 0; bIndex < sameSizeSet.length; bIndex++) {
         const bInst = sameSizeSet[bIndex];
-        if (implicit) bInst[memPos].flags.mem = true;
+        if (implicit)
+          bInst[memPos].flags.mem = true;
 
         if (!implicit)
           DEBUG(`${this.name}: Explicit: ${bInst}`);
@@ -1697,7 +1712,9 @@ class InstSignatureTable extends core.Task {
       }
     }
 
-    signatures.calcImplicitMemSize();
+    if (signatures.length && GenUtils.canUseImplicitMemSize(dbInsts[0].name))
+      signatures.calcImplicitMemSize();
+
     signatures.simplify();
     signatures.compact();