diff --git a/cozo-core/src/data/expr.rs b/cozo-core/src/data/expr.rs
index 5316f2a0..ef167fb0 100644
--- a/cozo-core/src/data/expr.rs
+++ b/cozo-core/src/data/expr.rs
@@ -88,11 +88,17 @@ pub fn eval_bytecode(
 ) -> Result<DataValue> {
     stack.clear();
     let mut pointer = 0;
+    // for (i, c) in bytecodes.iter().enumerate() {
+    //     println!("{i}  {c:?}");
+    // }
+    // println!();
     loop {
-        if pointer >= bytecodes.len() {
+        // println!("{pointer}  {stack:?}");
+        if pointer == bytecodes.len() {
             break;
         }
         let current_instruction = &bytecodes[pointer];
+        // println!("{current_instruction:?}");
         match current_instruction {
             Bytecode::Binding { var, tuple_pos, .. } => match tuple_pos {
                 None => {
diff --git a/cozo-core/src/data/tests/exprs.rs b/cozo-core/src/data/tests/exprs.rs
new file mode 100644
index 00000000..359f2c90
--- /dev/null
+++ b/cozo-core/src/data/tests/exprs.rs
@@ -0,0 +1,25 @@
+/*
+ * Copyright 2022, The Cozo Project Authors.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
+ * If a copy of the MPL was not distributed with this file,
+ * You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+use crate::{DataValue, new_cozo_mem};
+
+#[test]
+fn expression_eval() {
+    let db = new_cozo_mem().unwrap();
+
+
+    let res = db.run_script(r#"
+    ?[a] := a = if(2 + 3 > 1 * 99999, 190291021 + 14341234212 / 2121)
+    "#, Default::default()).unwrap();
+    assert_eq!(res.rows[0][0], DataValue::Null);
+
+    let res = db.run_script(r#"
+    ?[a] := a = if(2 + 3 > 1, true, false)
+    "#, Default::default()).unwrap();
+    assert_eq!(res.rows[0][0].get_bool().unwrap(), true);
+}
\ No newline at end of file
diff --git a/cozo-core/src/data/tests/mod.rs b/cozo-core/src/data/tests/mod.rs
index f673829f..194902d2 100644
--- a/cozo-core/src/data/tests/mod.rs
+++ b/cozo-core/src/data/tests/mod.rs
@@ -11,4 +11,5 @@ mod aggrs;
 mod validity;
 mod json;
 mod memcmp;
-mod values;
\ No newline at end of file
+mod values;
+mod exprs;
\ No newline at end of file
diff --git a/cozo-core/src/parse/expr.rs b/cozo-core/src/parse/expr.rs
index 867e6646..a973d100 100644
--- a/cozo-core/src/parse/expr.rs
+++ b/cozo-core/src/parse/expr.rs
@@ -71,18 +71,19 @@ pub(crate) fn expr2bytecode(expr: &Expr, collector: &mut Vec<Bytecode>) {
                 expr2bytecode(cond, collector);
                 // -1
                 collector.push(Bytecode::JumpIfFalse { jump_to: 0, span: *span });
-                let false_jump_amend_pos = collector.len();
+                let false_jump_amend_pos = collector.len() - 1;
                 // +1 in this branch
                 expr2bytecode(val, collector);
                 collector.push(Bytecode::Goto { jump_to: 0, span: *span });
-                return_jump_pos.push(collector.len());
+                return_jump_pos.push(collector.len() - 1);
                 collector[false_jump_amend_pos] = Bytecode::JumpIfFalse {
-                    jump_to: collector.len() + 1,
+                    jump_to: collector.len(),
                     span: *span,
                 };
             }
+            let total_len = collector.len();
             for pos in return_jump_pos {
-                collector[pos] = Bytecode::Goto { jump_to: pos, span: *span }
+                collector[pos] = Bytecode::Goto { jump_to: total_len, span: *span }
             }
         }
     }
@@ -267,11 +268,18 @@ fn build_term(pair: Pair<'_>, param_pool: &BTreeMap<String, DataValue>) -> Resul
 
             match ident {
                 "cond" => {
+                    if args.is_empty() {
+                        #[derive(Error, Diagnostic, Debug)]
+                        #[error("'cond' cannot have empty body")]
+                        #[diagnostic(code(parser::empty_cond))]
+                        struct EmptyCond(#[label] SourceSpan);
+                        bail!(EmptyCond(span));
+                    }
                     if args.len() & 1 == 1 {
                         args.insert(
                             args.len() - 1,
                             Expr::Const {
-                                val: DataValue::from(true),
+                                val: DataValue::Null,
                                 span: args.last().unwrap().span(),
                             },
                         )
@@ -280,16 +288,23 @@ fn build_term(pair: Pair<'_>, param_pool: &BTreeMap<String, DataValue>) -> Resul
                         .chunks(2)
                         .map(|pair| (pair[0].clone(), pair[1].clone()))
                         .collect_vec();
-                    clauses.push((
-                        Expr::Const {
-                            val: DataValue::from(true),
-                            span,
-                        },
-                        Expr::Const {
-                            val: DataValue::Null,
-                            span,
-                        },
-                    ));
+                    if let Some((cond, _)) = clauses.last() {
+                        match cond {
+                            Expr::Const { val: DataValue::Bool(true), ..} => {}
+                            _ => {
+                                clauses.push((
+                                    Expr::Const {
+                                        val: DataValue::from(true),
+                                        span,
+                                    },
+                                    Expr::Const {
+                                        val: DataValue::Null,
+                                        span,
+                                    },
+                                ));
+                            }
+                        }
+                    }
                     Expr::Cond { clauses, span }
                 }
                 "if" => {
@@ -311,7 +326,7 @@ fn build_term(pair: Pair<'_>, param_pool: &BTreeMap<String, DataValue>) -> Resul
                             span,
                         },
                         args.next().unwrap_or(Expr::Const {
-                            val: DataValue::from(true),
+                            val: DataValue::Null,
                             span,
                         }),
                     ));