diff --git a/src/frontend/mod.rs b/src/frontend/mod.rs
index a4a49e2a..f564598c 100644
--- a/src/frontend/mod.rs
+++ b/src/frontend/mod.rs
@@ -1,7 +1,11 @@
 //! The frontend includes the user-level abstractions and user-friendly types to define and work
 //! with Pods.
 
-use std::{collections::HashMap, convert::From, fmt};
+use std::{
+    collections::{HashMap, HashSet},
+    convert::From,
+    fmt,
+};
 
 use itertools::Itertools;
 use schemars::JsonSchema;
@@ -187,11 +191,11 @@ impl MainPodBuilder {
     }
 
     pub fn pub_op(&mut self, op: Operation) -> Result<Statement> {
-        self.op(true, op)
+        self.op(true, vec![], op)
     }
 
     pub fn priv_op(&mut self, op: Operation) -> Result<Statement> {
-        self.op(false, op)
+        self.op(false, vec![], op)
     }
 
     /// Lower syntactic sugar operation into backend compatible operation.
@@ -370,7 +374,17 @@ impl MainPodBuilder {
         }
     }
 
-    fn op_statement(&mut self, op: Operation) -> Result<Statement> {
+    fn op_statement(
+        &mut self,
+        wildcard_values: Vec<(usize, Value)>,
+        op: Operation,
+    ) -> Result<Statement> {
+        // Check for duplicate wildcard value assignments
+        let mut uniq = HashSet::new();
+        if !wildcard_values.iter().all(|(index, _)| uniq.insert(*index)) {
+            return Err(Error::custom("duplicate wildcard value assignments"));
+        }
+
         use NativeOperation::*;
         let st = match op.0 {
             OperationType::Native(o) => {
@@ -553,6 +567,16 @@ impl MainPodBuilder {
 
                 let mut wildcard_map =
                     vec![Option::None; self.params.max_custom_predicate_wildcards];
+                for (index, value) in wildcard_values.into_iter() {
+                    if index >= wildcard_map.len() {
+                        return Err(Error::custom(format!(
+                            "wildcard index {} greater-equal than max {}",
+                            index,
+                            wildcard_map.len() - 1,
+                        )));
+                    }
+                    wildcard_map[index] = Some(value);
+                }
                 for (st_tmpl, st) in pred.statements.iter().zip(args.iter()) {
                     let st_args = st.args();
                     for (st_tmpl_arg, st_arg) in st_tmpl.args.iter().zip(&st_args) {
@@ -601,10 +625,16 @@ impl MainPodBuilder {
         Ok(())
     }
 
-    fn op(&mut self, public: bool, op: Operation) -> Result<Statement> {
+    /// `wildcard_values`: wildcard values to use instead of EMPTY_VALUE for unresolved wildcards
+    pub fn op(
+        &mut self,
+        public: bool,
+        wildcard_values: Vec<(usize, Value)>,
+        op: Operation,
+    ) -> Result<Statement> {
         self.add_entries_contains(&op)?;
         let op = Self::fill_in_aux(Self::lower_op(op)?)?;
-        let st = self.op_statement(op.clone())?;
+        let st = self.op_statement(wildcard_values, op.clone())?;
         self.insert(public, (st, op))?;
 
         Ok(self.statements[self.statements.len() - 1].clone())
@@ -772,6 +802,7 @@ pub mod tests {
             tickets_pod_full_flow, zu_kyc_pod_builder, zu_kyc_pod_request,
             zu_kyc_sign_dict_builders, EthDosHelper, MOCK_VD_SET,
         },
+        lang::parse,
         middleware::{
             containers::{Array, Set},
             Signer as _, Value,
@@ -930,7 +961,7 @@ pub mod tests {
             ],
             OperationAux::None,
         );
-        let st1 = builder.op(true, op_eq1).unwrap();
+        let st1 = builder.op(true, vec![], op_eq1).unwrap();
         let op_eq2 = Operation(
             OperationType::Native(NativeOperation::EqualFromEntries),
             vec![
@@ -939,14 +970,14 @@ pub mod tests {
             ],
             OperationAux::None,
         );
-        let st2 = builder.op(true, op_eq2).unwrap();
+        let st2 = builder.op(true, vec![], op_eq2).unwrap();
 
         let op_eq3 = Operation(
             OperationType::Native(NativeOperation::TransitiveEqualFromStatements),
             vec![OperationArg::Statement(st1), OperationArg::Statement(st2)],
             OperationAux::None,
         );
-        builder.op(true, op_eq3).unwrap();
+        builder.op(true, vec![], op_eq3).unwrap();
 
         let prover = MockProver {};
         let pod = builder.prove(&prover).unwrap();
@@ -1006,7 +1037,7 @@ pub mod tests {
         let st0 = signed_dict.get_statement("dict").unwrap();
         let local = dict!(32, {"key" => "a"})?;
         let st1 = builder
-            .op(true, Operation::dict_contains(local, "key", "a"))
+            .op(true, vec![], Operation::dict_contains(local, "key", "a"))
             .unwrap();
 
         builder.pub_op(Operation(
@@ -1228,6 +1259,7 @@ pub mod tests {
         let st1 = builder
             .op(
                 true,
+                vec![],
                 Operation::dict_contains(local, "known_secret", SecretKey(BigUint::from(123u32))),
             )
             .unwrap();
@@ -1327,4 +1359,40 @@ pub mod tests {
         let pod = builder.prove(&prover).unwrap();
         pod.pod.verify().unwrap();
     }
+
+    #[test]
+    fn test_wildcard_values() -> Result<()> {
+        let params = Params::default();
+        let vd_set = &*MOCK_VD_SET;
+
+        let input = r#"
+        Test(a, b) = OR(
+            Equal(a, 5)
+            Equal(b, 5)
+        )
+        "#;
+        let batch = parse(input, &params, &[]).unwrap().custom_batch;
+        let pred_test = batch.predicate_ref_by_name("Test").unwrap();
+
+        // Try to build with wrong type in 1st arg
+        let mut builder = MainPodBuilder::new(&params, vd_set);
+        let st0 = builder.priv_op(Operation::eq(5, 5)).unwrap();
+        let wildcard_values = vec![(1, Value::from(42))];
+        let st = builder
+            .op(
+                true,
+                wildcard_values,
+                Operation::custom(pred_test, [st0, Statement::None]),
+            )
+            .unwrap();
+        let st_args = st.args();
+        assert_eq!(StatementArg::Literal(Value::from(5)), st_args[0]);
+        assert_eq!(StatementArg::Literal(Value::from(42)), st_args[1]);
+
+        let prover = MockProver {};
+        let pod = builder.prove(&prover).unwrap();
+        pod.pod.verify().unwrap();
+
+        Ok(())
+    }
 }