diff --git a/src/arch/x86_64/encode.rs b/src/arch/x86_64/encode.rs
index 978ab44..b3674bb 100644
--- a/src/arch/x86_64/encode.rs
+++ b/src/arch/x86_64/encode.rs
@@ -172,7 +172,7 @@ impl Code {
         self.bytes.push(0xc3);
     }
 
-    pub fn sub(&mut self, dst: Reg, src: impl Into<Imm>) -> ERes {
+    fn add_sub(&mut self, dst: Reg, src: impl Into<Imm>, ext: u8) -> ERes {
         let mut src = src.into();
         let mut width = src.width_signed()?;
         let dst_width = dst.width().min(Width::B32);
@@ -198,11 +198,19 @@ impl Code {
             width = dst_width;
         }
 
-        self.bytes.push(modrm(0b11, 0b101, dst.base()));
+        self.bytes.push(modrm(0b11, ext, dst.base()));
         self.imm(src, width);
         Ok(())
     }
 
+    pub fn add(&mut self, dst: Reg, src: impl Into<Imm>) -> ERes {
+        self.add_sub(dst, src, 0)
+    }
+
+    pub fn sub(&mut self, dst: Reg, src: impl Into<Imm>) -> ERes {
+        self.add_sub(dst, src, 5)
+    }
+
     fn prefix16(&mut self, width: impl Into<Width>) {
         if width.into() == Width::B16 {
             self.bytes.push(0x66);
diff --git a/src/arch/x86_64/test/asm/mod.rs b/src/arch/x86_64/test/asm/mod.rs
index e84f419..9cd7a02 100644
--- a/src/arch/x86_64/test/asm/mod.rs
+++ b/src/arch/x86_64/test/asm/mod.rs
@@ -37,9 +37,15 @@ fn mov() {
 }
 
 #[test]
-fn sub() {
+fn add_sub() {
     let c = &mut TestCtx::new("mov");
 
+    for dst in regs() {
+        for src in imms() {
+            eq(c, format!("add {dst}, {src}"), |c| c.add(dst, src))
+        }
+    }
+
     for dst in regs() {
         for src in imms() {
             eq(c, format!("sub {dst}, {src}"), |c| c.sub(dst, src))
diff --git a/test/nasm_cache/mov b/test/nasm_cache/mov
index b65b4cb..9e836a3 100644
Binary files a/test/nasm_cache/mov and b/test/nasm_cache/mov differ