diff --git a/ujit_codegen.c b/ujit_codegen.c
index bb0b802fc4..e45005a70e 100644
--- a/ujit_codegen.c
+++ b/ujit_codegen.c
@@ -570,9 +570,9 @@ gen_opt_lt(jitstate_t* jit, ctx_t* ctx)
     }
 
     // Compare the arguments
-    mov(cb, REG0, arg0);
-    cmp(cb, REG0, arg1);
-    mov(cb, REG0, imm_opnd(Qfalse));
+    xor(cb, REG0_32, REG0_32); // REG0 = Qfalse
+    mov(cb, REG1, arg0);
+    cmp(cb, REG1, arg1);
     mov(cb, REG1, imm_opnd(Qtrue));
     cmovl(cb, REG0, REG1);
 
diff --git a/ujit_core.h b/ujit_core.h
index 7b230d779d..c86a9412dc 100644
--- a/ujit_core.h
+++ b/ujit_core.h
@@ -35,10 +35,10 @@ typedef struct CtxStruct
     uint8_t temp_types[MAX_TEMP_TYPES];
 
     // Number of values pushed on the temporary stack
-    uint32_t stack_size;
+    uint16_t stack_size;
 
     // Whether we know self is a heap object
-    bool self_is_object;
+    bool self_is_object : 1;
 
 } ctx_t;