diff --git a/src/classic/clvm/mod.rs b/src/classic/clvm/mod.rs
index 0c54c0087..bb269fa56 100644
--- a/src/classic/clvm/mod.rs
+++ b/src/classic/clvm/mod.rs
@@ -20,7 +20,7 @@ struct KwAtomPair {
     version: usize,
 }
 
-const KW_PAIRS: [KwAtomPair; 46] = [
+const KW_PAIRS: [KwAtomPair; 48] = [
     KwAtomPair {
         v: &[0x01],
         n: "q",
@@ -241,6 +241,16 @@ const KW_PAIRS: [KwAtomPair; 46] = [
         n: "bls_verify",
         version: 1,
     },
+    KwAtomPair {
+        v: &[0x3c],
+        n: "modpow",
+        version: 1,
+    },
+    KwAtomPair {
+        v: &[0x3d],
+        n: "%",
+        version: 1,
+    },
     KwAtomPair {
         v: &[0x13, 0xd6, 0x1f, 0x00],
         n: "secp256k1_verify",
diff --git a/src/compiler/prims.rs b/src/compiler/prims.rs
index 8a30023b2..4b51554c3 100644
--- a/src/compiler/prims.rs
+++ b/src/compiler/prims.rs
@@ -187,6 +187,14 @@ pub fn prims() -> Vec<(Vec<u8>, SExp)> {
             "bls_verify".as_bytes().to_vec(),
             SExp::Integer(primloc.clone(), 59_u32.to_bigint().unwrap()),
         ),
+        (
+            "modpow".as_bytes().to_vec(),
+            SExp::Integer(primloc.clone(), 60_u32.to_bigint().unwrap()),
+        ),
+        (
+            "%".as_bytes().to_vec(),
+            SExp::Integer(primloc.clone(), 61_u32.to_bigint().unwrap()),
+        ),
         (
             "secp256k1_verify".as_bytes().to_vec(),
             SExp::Integer(primloc.clone(), 0x13d61f00.to_bigint().unwrap()),
diff --git a/src/tests/classic/run.rs b/src/tests/classic/run.rs
index 410e4060d..702efd80d 100644
--- a/src/tests/classic/run.rs
+++ b/src/tests/classic/run.rs
@@ -2429,6 +2429,50 @@ fn test_assign_cse_tricky_2() {
     assert_eq!(program, wanted_repr);
 }
 
+#[test]
+fn test_classic_modpow() {
+    let result = do_basic_brun(&vec![
+        "brun".to_string(),
+        "(modpow (q . 2) (q . 6) (q . 5))".to_string(),
+    ]);
+    // 64 % 5 == 4
+    assert_eq!(result.trim(), "4");
+}
+
+#[test]
+fn test_classic_mod_op() {
+    let result = do_basic_brun(&vec![
+        "brun".to_string(),
+        "(% (q . 13) (q . 10))".to_string(),
+    ]);
+    // 13 % 10 == 3
+    assert_eq!(result.trim(), "3");
+}
+
+#[test]
+fn test_modern_modpow() {
+    let program = do_basic_run(&vec![
+        "run".to_string(),
+        "(mod (X Y Z) (include *standard-cl-23*) (modpow X Y Z))".to_string(),
+    ]);
+    assert_eq!(program.trim(), "(60 2 5 11)");
+    let result = do_basic_brun(&vec!["brun".to_string(), program, "(2 7 10)".to_string()]);
+    // 128 % 10 == 8
+    assert_eq!(result.trim(), "8");
+}
+
+#[test]
+fn test_modern_mod_op() {
+    let program = do_basic_run(&vec![
+        "run".to_string(),
+        "(mod (X Y) (include *standard-cl-23*) (% X Y))".to_string(),
+    ]);
+    assert_eq!(program.trim(), "(61 2 5)");
+    let result = do_basic_brun(&vec!["brun".to_string(), program, "(137 6)".to_string()]);
+    // 137 % 6 == 5
+    assert_eq!(result.trim(), "5");
+}
+
 #[test]
 fn test_include_zero_bin() {
     let program = do_basic_run(&vec![