diff --git a/compiler/gen_dev/src/generic64/aarch64.rs b/compiler/gen_dev/src/generic64/aarch64.rs
index d344be324c..890995c726 100644
--- a/compiler/gen_dev/src/generic64/aarch64.rs
+++ b/compiler/gen_dev/src/generic64/aarch64.rs
@@ -500,6 +500,16 @@ impl Assembler<AArch64GeneralReg, AArch64FloatReg> for AArch64Assembler {
         unimplemented!("registers non-equality not implemented yet for AArch64");
     }
 
+    #[inline(always)]
+    fn lt_reg64_reg64_reg64(
+        _buf: &mut Vec<'_, u8>,
+        _dst: AArch64GeneralReg,
+        _src1: AArch64GeneralReg,
+        _src2: AArch64GeneralReg,
+    ) {
+        unimplemented!("registers less than not implemented yet for AArch64");
+    }
+
     #[inline(always)]
     fn ret(buf: &mut Vec<'_, u8>) {
         ret_reg64(buf, AArch64GeneralReg::LR)
diff --git a/compiler/gen_dev/src/generic64/mod.rs b/compiler/gen_dev/src/generic64/mod.rs
index dbffdcf8f4..b3936857b9 100644
--- a/compiler/gen_dev/src/generic64/mod.rs
+++ b/compiler/gen_dev/src/generic64/mod.rs
@@ -179,6 +179,13 @@ pub trait Assembler<GeneralReg: RegTrait, FloatReg: RegTrait> {
         src2: GeneralReg,
     );
 
+    fn lt_reg64_reg64_reg64(
+        buf: &mut Vec<'_, u8>,
+        dst: GeneralReg,
+        src1: GeneralReg,
+        src2: GeneralReg,
+    );
+
     fn ret(buf: &mut Vec<'_, u8>);
 }
 
@@ -868,6 +875,25 @@ impl<
         }
     }
 
+    fn build_num_lt(
+        &mut self,
+        dst: &Symbol,
+        src1: &Symbol,
+        src2: &Symbol,
+        arg_layout: &Layout<'a>,
+    ) -> Result<(), String> {
+        match arg_layout {
+            Layout::Builtin(Builtin::Int64) => {
+                let dst_reg = self.claim_general_reg(dst)?;
+                let src1_reg = self.load_to_general_reg(src1)?;
+                let src2_reg = self.load_to_general_reg(src2)?;
+                ASM::lt_reg64_reg64_reg64(&mut self.buf, dst_reg, src1_reg, src2_reg);
+                Ok(())
+            }
+            x => Err(format!("NumLt: layout, {:?}, not implemented yet", x)),
+        }
+    }
+
     fn create_struct(
         &mut self,
         sym: &Symbol,
diff --git a/compiler/gen_dev/src/generic64/x86_64.rs b/compiler/gen_dev/src/generic64/x86_64.rs
index d5e1b134cb..ce052c7448 100644
--- a/compiler/gen_dev/src/generic64/x86_64.rs
+++ b/compiler/gen_dev/src/generic64/x86_64.rs
@@ -1107,6 +1107,17 @@ impl Assembler<X86_64GeneralReg, X86_64FloatReg> for X86_64Assembler {
         setne_reg64(buf, dst);
     }
 
+    #[inline(always)]
+    fn lt_reg64_reg64_reg64(
+        buf: &mut Vec<'_, u8>,
+        dst: X86_64GeneralReg,
+        src1: X86_64GeneralReg,
+        src2: X86_64GeneralReg,
+    ) {
+        cmp_reg64_reg64(buf, src1, src2);
+        setl_reg64(buf, dst);
+    }
+
     #[inline(always)]
     fn ret(buf: &mut Vec<'_, u8>) {
         ret(buf);
@@ -1498,6 +1509,12 @@ fn setne_reg64(buf: &mut Vec<'_, u8>, reg: X86_64GeneralReg) {
     set_reg64_help(buf, reg, 0x95);
 }
 
+/// `SETL r/m64` -> Set byte if less (SF≠ OF).
+#[inline(always)]
+fn setl_reg64(buf: &mut Vec<'_, u8>, reg: X86_64GeneralReg) {
+    set_reg64_help(buf, reg, 0x9c);
+}
+
 /// `RET` -> Near return to calling procedure.
 #[inline(always)]
 fn ret(buf: &mut Vec<'_, u8>) {
diff --git a/compiler/gen_dev/src/lib.rs b/compiler/gen_dev/src/lib.rs
index e8dff1d967..a87e2ecdf7 100644
--- a/compiler/gen_dev/src/lib.rs
+++ b/compiler/gen_dev/src/lib.rs
@@ -433,6 +433,23 @@ where
                 );
                 self.build_neq(sym, &args[0], &args[1], &arg_layouts[0])
             }
+            LowLevel::NumLt => {
+                debug_assert_eq!(
+                    2,
+                    args.len(),
+                    "NumLt: expected to have exactly two argument"
+                );
+                debug_assert_eq!(
+                    arg_layouts[0], arg_layouts[1],
+                    "NumLt: expected all arguments of to have the same layout"
+                );
+                debug_assert_eq!(
+                    Layout::Builtin(Builtin::Int1),
+                    *ret_layout,
+                    "NumLt: expected to have return layout of type I1"
+                );
+                self.build_num_lt(sym, &args[0], &args[1], &arg_layouts[0])
+            }
             LowLevel::NumRound => self.build_fn_call(
                 sym,
                 bitcode::NUM_ROUND[FloatWidth::F64].to_string(),
@@ -523,6 +540,15 @@ where
         arg_layout: &Layout<'a>,
     ) -> Result<(), String>;
 
+    /// build_num_lt stores the result of `src1 < src2` into dst.
+    fn build_num_lt(
+        &mut self,
+        dst: &Symbol,
+        src1: &Symbol,
+        src2: &Symbol,
+        arg_layout: &Layout<'a>,
+    ) -> Result<(), String>;
+
     /// literal_map gets the map from symbol to literal, used for lazy loading and literal folding.
     fn literal_map(&mut self) -> &mut MutMap<Symbol, Literal<'a>>;
 
diff --git a/compiler/test_gen/src/gen_num.rs b/compiler/test_gen/src/gen_num.rs
index df451c4898..1c283bac43 100644
--- a/compiler/test_gen/src/gen_num.rs
+++ b/compiler/test_gen/src/gen_num.rs
@@ -726,6 +726,20 @@ fn gen_int_neq() {
     );
 }
 
+#[test]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm", feature = "gen-dev"))]
+fn gen_int_less_than() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+                    4 < 5
+                "#
+        ),
+        true,
+        bool
+    );
+}
+
 #[test]
 #[cfg(any(feature = "gen-llvm"))]
 fn gen_dec_eq() {