diff --git a/tool/generation_test/fixtures/many_param/input.dart b/tool/generation_test/fixtures/many_param/input.dart
new file mode 100644
index 0000000..4e6e003
--- /dev/null
+++ b/tool/generation_test/fixtures/many_param/input.dart
@@ -0,0 +1,29 @@
+import 'package:genq/genq.dart';
+
+part 'input.genq.dart';
+
+@genq
+class ManyParams with _$ManyParams {
+  factory ManyParams({
+    required int a,
+    required int b,
+    required int c,
+    required int d,
+    required int e,
+    required int f,
+    required int g,
+    required int h,
+    required int i,
+    required int j,
+    required int k,
+    required int l,
+    required int m,
+    required int n,
+    required int o,
+    required int p,
+    required int q,
+    required int r,
+    required int s,
+    required int t,
+  }) = _ManyParams;
+}
diff --git a/tool/generation_test/fixtures/many_param/input.genq.dart b/tool/generation_test/fixtures/many_param/input.genq.dart
new file mode 100644
index 0000000..d4de2ba
--- /dev/null
+++ b/tool/generation_test/fixtures/many_param/input.genq.dart
@@ -0,0 +1,251 @@
+part of 'input.dart';
+
+mixin _$ManyParams {
+  int get a => throw UnimplementedError();
+  int get b => throw UnimplementedError();
+  int get c => throw UnimplementedError();
+  int get d => throw UnimplementedError();
+  int get e => throw UnimplementedError();
+  int get f => throw UnimplementedError();
+  int get g => throw UnimplementedError();
+  int get h => throw UnimplementedError();
+  int get i => throw UnimplementedError();
+  int get j => throw UnimplementedError();
+  int get k => throw UnimplementedError();
+  int get l => throw UnimplementedError();
+  int get m => throw UnimplementedError();
+  int get n => throw UnimplementedError();
+  int get o => throw UnimplementedError();
+  int get p => throw UnimplementedError();
+  int get q => throw UnimplementedError();
+  int get r => throw UnimplementedError();
+  int get s => throw UnimplementedError();
+  int get t => throw UnimplementedError();
+
+  $ManyParamsCopyWith get copyWith => throw UnimplementedError();
+}
+
+class _ManyParams implements ManyParams {
+  @override
+  final int a;
+
+  @override
+  final int b;
+
+  @override
+  final int c;
+
+  @override
+  final int d;
+
+  @override
+  final int e;
+
+  @override
+  final int f;
+
+  @override
+  final int g;
+
+  @override
+  final int h;
+
+  @override
+  final int i;
+
+  @override
+  final int j;
+
+  @override
+  final int k;
+
+  @override
+  final int l;
+
+  @override
+  final int m;
+
+  @override
+  final int n;
+
+  @override
+  final int o;
+
+  @override
+  final int p;
+
+  @override
+  final int q;
+
+  @override
+  final int r;
+
+  @override
+  final int s;
+
+  @override
+  final int t;
+
+  _ManyParams({
+    required this.a,
+    required this.b,
+    required this.c,
+    required this.d,
+    required this.e,
+    required this.f,
+    required this.g,
+    required this.h,
+    required this.i,
+    required this.j,
+    required this.k,
+    required this.l,
+    required this.m,
+    required this.n,
+    required this.o,
+    required this.p,
+    required this.q,
+    required this.r,
+    required this.s,
+    required this.t,
+  });
+
+  @override
+  $ManyParamsCopyWith get copyWith => _$ManyParamsCopyWithImpl(this);
+
+  @override
+  String toString() {
+    return "ManyParams(a: $a, b: $b, c: $c, d: $d, e: $e, f: $f, g: $g, h: $h, i: $i, j: $j, k: $k, l: $l, m: $m, n: $n, o: $o, p: $p, q: $q, r: $r, s: $s, t: $t)";
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) return true;
+    if (other is! ManyParams) return false;
+    if (!identical(other.a, a) && other.a != a) return false;
+    if (!identical(other.b, b) && other.b != b) return false;
+    if (!identical(other.c, c) && other.c != c) return false;
+    if (!identical(other.d, d) && other.d != d) return false;
+    if (!identical(other.e, e) && other.e != e) return false;
+    if (!identical(other.f, f) && other.f != f) return false;
+    if (!identical(other.g, g) && other.g != g) return false;
+    if (!identical(other.h, h) && other.h != h) return false;
+    if (!identical(other.i, i) && other.i != i) return false;
+    if (!identical(other.j, j) && other.j != j) return false;
+    if (!identical(other.k, k) && other.k != k) return false;
+    if (!identical(other.l, l) && other.l != l) return false;
+    if (!identical(other.m, m) && other.m != m) return false;
+    if (!identical(other.n, n) && other.n != n) return false;
+    if (!identical(other.o, o) && other.o != o) return false;
+    if (!identical(other.p, p) && other.p != p) return false;
+    if (!identical(other.q, q) && other.q != q) return false;
+    if (!identical(other.r, r) && other.r != r) return false;
+    if (!identical(other.s, s) && other.s != s) return false;
+    if (!identical(other.t, t) && other.t != t) return false;
+    return true;
+  }
+
+  @override
+  int get hashCode {
+    return Object.hashAll([
+      runtimeType,
+      a,
+      b,
+      c,
+      d,
+      e,
+      f,
+      g,
+      h,
+      i,
+      j,
+      k,
+      l,
+      m,
+      n,
+      o,
+      p,
+      q,
+      r,
+      s,
+      t,
+    ]);
+  }
+}
+
+abstract class $ManyParamsCopyWith {
+  ManyParams call({
+    int a,
+    int b,
+    int c,
+    int d,
+    int e,
+    int f,
+    int g,
+    int h,
+    int i,
+    int j,
+    int k,
+    int l,
+    int m,
+    int n,
+    int o,
+    int p,
+    int q,
+    int r,
+    int s,
+    int t,
+  });
+}
+
+class _$ManyParamsCopyWithImpl implements $ManyParamsCopyWith {
+  final _$ManyParams value;
+
+  _$ManyParamsCopyWithImpl(this.value);
+
+  @override
+  ManyParams call({
+    Object? a = genq,
+    Object? b = genq,
+    Object? c = genq,
+    Object? d = genq,
+    Object? e = genq,
+    Object? f = genq,
+    Object? g = genq,
+    Object? h = genq,
+    Object? i = genq,
+    Object? j = genq,
+    Object? k = genq,
+    Object? l = genq,
+    Object? m = genq,
+    Object? n = genq,
+    Object? o = genq,
+    Object? p = genq,
+    Object? q = genq,
+    Object? r = genq,
+    Object? s = genq,
+    Object? t = genq,
+  }) {
+    return ManyParams(
+      a: a == genq ? value.a : a as int,
+      b: b == genq ? value.b : b as int,
+      c: c == genq ? value.c : c as int,
+      d: d == genq ? value.d : d as int,
+      e: e == genq ? value.e : e as int,
+      f: f == genq ? value.f : f as int,
+      g: g == genq ? value.g : g as int,
+      h: h == genq ? value.h : h as int,
+      i: i == genq ? value.i : i as int,
+      j: j == genq ? value.j : j as int,
+      k: k == genq ? value.k : k as int,
+      l: l == genq ? value.l : l as int,
+      m: m == genq ? value.m : m as int,
+      n: n == genq ? value.n : n as int,
+      o: o == genq ? value.o : o as int,
+      p: p == genq ? value.p : p as int,
+      q: q == genq ? value.q : q as int,
+      r: r == genq ? value.r : r as int,
+      s: s == genq ? value.s : s as int,
+      t: t == genq ? value.t : t as int,
+    );
+  }
+}
\ No newline at end of file
diff --git a/tool/generation_test/gen_test.go b/tool/generation_test/gen_test.go
index d6a99ab..36bbc2b 100644
--- a/tool/generation_test/gen_test.go
+++ b/tool/generation_test/gen_test.go
@@ -92,3 +92,7 @@ func TestJsonCollections(t *testing.T) {
 func TestSealedClasses(t *testing.T) {
 	testGenOutput(t, "sealed_classes")
 }
+
+func TestManyParam(t *testing.T) {
+	testGenOutput(t, "many_param")
+}
diff --git a/tool/templates/scaffold.go b/tool/templates/scaffold.go
index f09c23b..cce541c 100644
--- a/tool/templates/scaffold.go
+++ b/tool/templates/scaffold.go
@@ -103,12 +103,24 @@ func templateConstructor(str []string, classDecl GenqClassDeclaration) []string
 	str = append(str, indent(2, fmt.Sprintf("int get hashCode {")))
 
 	if len(classDecl.Constructor.ParamList.NamedParams) > 0 {
-		str = append(str, indent(4, fmt.Sprintf("return Object.hash(")))
-		str = append(str, indent(6, "runtimeType,"))
-		for _, param := range classDecl.Constructor.ParamList.NamedParams {
-			str = append(str, indent(6, fmt.Sprintf("%s,", param.Name)))
+		// The +1 is for the runtimeType
+		totalParamCount := len(classDecl.Constructor.ParamList.NamedParams) + 1
+		if totalParamCount > 20 {
+			str = append(str, indent(4, fmt.Sprintf("return Object.hashAll([")))
+			str = append(str, indent(6, "runtimeType,"))
+			for _, param := range classDecl.Constructor.ParamList.NamedParams {
+				str = append(str, indent(6, fmt.Sprintf("%s,", param.Name)))
+			}
+			str = append(str, indent(4, fmt.Sprintf("]);")))
+		} else {
+			str = append(str, indent(4, fmt.Sprintf("return Object.hash(")))
+			str = append(str, indent(6, "runtimeType,"))
+			for _, param := range classDecl.Constructor.ParamList.NamedParams {
+				str = append(str, indent(6, fmt.Sprintf("%s,", param.Name)))
+			}
+			str = append(str, indent(4, fmt.Sprintf(");")))
 		}
-		str = append(str, indent(4, fmt.Sprintf(");")))
+
 	} else {
 		str = append(str, indent(4, fmt.Sprintf("return runtimeType.hashCode;")))
 	}