diff --git a/src/sql/src/plan/typeconv.rs b/src/sql/src/plan/typeconv.rs
index c4abe14723a1e..60cbe2dd5e04e 100644
--- a/src/sql/src/plan/typeconv.rs
+++ b/src/sql/src/plan/typeconv.rs
@@ -18,7 +18,6 @@ use dynfmt::{Format, SimpleCurlyFormat};
 use itertools::Itertools;
 use mz_expr::func::{CastArrayToJsonb, CastListToJsonb};
 use mz_expr::{VariadicFunc, func};
-use mz_ore::assert_none;
 use mz_repr::{ColumnName, ColumnType, Datum, RelationType, ScalarBaseType, ScalarType};
 
 use crate::catalog::TypeCategory;
@@ -1134,7 +1133,16 @@ pub fn plan_coerce<'a>(
 
         Parameter(n) => {
             let prev = ecx.param_types().borrow_mut().insert(n, coerce_to.clone());
-            assert_none!(prev);
+            if let Some(prev) = prev {
+                if prev != *coerce_to {
+                    sql_bail!(
+                        "there are contradicting constraints for the type of parameter ${}: should be both {} and {}",
+                        n,
+                        ecx.humanize_scalar_type(&prev, false),
+                        ecx.humanize_scalar_type(coerce_to, false),
+                    );
+                }
+            }
             HirScalarExpr::parameter(n)
         }
     })
diff --git a/test/sqllogictest/prepare.slt b/test/sqllogictest/prepare.slt
index 6a36bf058bb73..a6dcfc0d79fb0 100644
--- a/test/sqllogictest/prepare.slt
+++ b/test/sqllogictest/prepare.slt
@@ -60,3 +60,63 @@ SELECT * FROM t;
 4
 5
 6
+
+statement ok
+PREPARE p1 AS
+SELECT $1 + $1::bigint;
+
+query I
+EXECUTE p1(5);
+----
+10
+
+statement ok
+PREPARE p2 AS
+SELECT $1::bigint + $1::bigint;
+
+query I
+EXECUTE p2(7);
+----
+14
+
+statement ok
+PREPARE p3 AS
+SELECT $1 || $1;
+
+query T
+EXECUTE p3('abc');
+----
+abcabc
+
+statement ok
+PREPARE p4 AS
+SELECT $1::text || $1::bigint::text;
+
+query error db error: ERROR: invalid input syntax for type bigint: invalid digit found in string: "abc"
+EXECUTE p4('abc');
+
+query T
+EXECUTE p4('123');
+----
+123123
+
+statement ok
+PREPARE p5 AS
+SELECT $1, $1::bigint;
+
+query II
+EXECUTE p5(7);
+----
+0
+7
+
+query error db error: ERROR: operator does not exist: bigint \|\| bigint
+PREPARE p6 AS
+SELECT $1 + $1::bigint, $1 || $1;
+
+query error db error: ERROR: operator does not exist: text \+ bigint
+PREPARE p7 AS
+SELECT $1 || $1, $1 + $1::bigint;
+
+query error db error: ERROR: there are contradicting constraints for the type of parameter \$1: should be both text and integer
+PREPARE p AS SELECT repeat($1, $1);