diff --git a/src/thingdef/thingdef_expression.cpp b/src/thingdef/thingdef_expression.cpp
index 2395b0d0eb..f95bfcdafd 100644
--- a/src/thingdef/thingdef_expression.cpp
+++ b/src/thingdef/thingdef_expression.cpp
@@ -2203,17 +2203,25 @@ ExpEmit FxPick::Emit(VMFunctionBuilder *build)
 	for (unsigned i = 0; i < choices.Size(); ++i)
 	{
 		build->BackpatchToHere(jumptable + i);
-		ExpEmit casereg = choices[i]->Emit(build);
-		if (casereg.RegNum != resultreg.RegNum)
-		{ // The result of the case is in a different register from what
-		  // was expected. Copy it to the one we wanted.
-
-			resultreg.Reuse(build);	// This is really just for the assert in Reuse()
-			build->Emit(OP_MOVE, resultreg.RegNum, casereg.RegNum, 0);
-			resultreg.Free(build);
+		if (choices[i]->isConstant())
+		{
+			int val = static_cast<FxConstant *>(choices[i])->GetValue().GetInt();
+			build->EmitLoadInt(resultreg.RegNum, val);
+		}
+		else
+		{
+			ExpEmit casereg = choices[i]->Emit(build);
+			if (casereg.RegNum != resultreg.RegNum)
+			{ // The result of the case is in a different register from what
+			  // was expected. Copy it to the one we wanted.
+
+				resultreg.Reuse(build);	// This is really just for the assert in Reuse()
+				build->Emit(OP_MOVE, resultreg.RegNum, casereg.RegNum, 0);
+				resultreg.Free(build);
+			}
+			// Free this register so the remaining cases can use it.
+			casereg.Free(build);
 		}
-		// Free this register so the remaining cases can use it.
-		casereg.Free(build);
 		// All but the final case needs a jump to the end of the expression's code.
 		if (i + 1 < choices.Size())
 		{
diff --git a/src/zscript/vmbuilder.cpp b/src/zscript/vmbuilder.cpp
index 2dff77cfcc..d17efc1d98 100644
--- a/src/zscript/vmbuilder.cpp
+++ b/src/zscript/vmbuilder.cpp
@@ -423,8 +423,9 @@ void VMFunctionBuilder::RegAvailability::Return(int reg, int count)
 bool VMFunctionBuilder::RegAvailability::Reuse(int reg)
 {
 	assert(reg >= 0 && reg <= 255);
+	assert(reg < MostUsed && "Attempt to reuse a register that was never used");
 
-	VM_UWORD mask = reg & 31;
+	VM_UWORD mask = 1 << (reg & 31);
 	int word = reg / 32;
 
 	if (Used[word] & mask)