diff --git a/expr_json.go b/expr_json.go
index a81b5f4bd..91cd8ed4e 100644
--- a/expr_json.go
+++ b/expr_json.go
@@ -21,7 +21,9 @@ import (
 	"bytes"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"io"
 	"math"
 	"sort"
 	"strings"
@@ -488,8 +490,21 @@ func decodeExpr(raw json.RawMessage, schema *Schema, caseSensitive bool) (Boolea
 // without inspecting bytes by hand.
 func firstToken(raw json.RawMessage) (json.Token, error) {
 	dec := json.NewDecoder(bytes.NewReader(raw))
+	tok, err := dec.Token()
+	if err != nil {
+		return nil, err
+	}
+	if _, ok := tok.(bool); ok {
+		if _, err := dec.Token(); !errors.Is(err, io.EOF) {
+			if err == nil {
+				return nil, errors.New("trailing data after boolean expression")
+			}
+
+			return nil, err
+		}
+	}
 
-	return dec.Token()
+	return tok, nil
 }
 
 func decodePredicate(op Operation, node exprNode, schema *Schema, caseSensitive bool) (BooleanExpression, error) {
diff --git a/expr_json_test.go b/expr_json_test.go
index b5841a4b8..1b9de31d6 100644
--- a/expr_json_test.go
+++ b/expr_json_test.go
@@ -393,6 +393,20 @@ func TestUnmarshalExpressionErrors(t *testing.T) {
 	}
 }
 
+func TestUnmarshalBooleanExpressionRejectsTrailingData(t *testing.T) {
+	for _, input := range []string{
+		`true false`,
+		`false null`,
+		`true{}`,
+		`false garbage`,
+	} {
+		t.Run(input, func(t *testing.T) {
+			_, err := iceberg.ParseExpr([]byte(input), nil)
+			require.ErrorIs(t, err, iceberg.ErrInvalidArgument)
+		})
+	}
+}
+
 // TestExpressionTransformTermRoundTrip covers a residual filter whose term is a
 // partition transform, e.g. a Java server's bucket[100](id) <= 50.
 func TestExpressionTransformTermRoundTrip(t *testing.T) {