diff --git a/Changes b/Changes
index 72c929dc7..d8f1d20b5 100644
--- a/Changes
+++ b/Changes
@@ -17,6 +17,7 @@ Verilator 5.037 devel
 * Support constrained random for associative arrays (#5985) (#5986). [Yilou Wang]
 * Support assignments to concatenations with impure RHS (#6002). [Ryszard Rozak, Antmicro Ltd.]
 * Support SARIF JSON diagnostic output with `--diagnostics-sarif`. (#6017)
+* Support parameter forward types.
 * Add BADVLTPRAGMA on unknown Verilator pragmas (#5945). [Shou-Li Hsu]
 * Add PROCINITASSIGN on initial assignments to process variables (#2481). [Niraj Menon]
 * Fix filename backslash escapes in C code (#5947).
diff --git a/src/V3Ast.h b/src/V3Ast.h
index 2a4f84617..46a0c6f0d 100644
--- a/src/V3Ast.h
+++ b/src/V3Ast.h
@@ -287,6 +287,33 @@ public:
 
 // ######################################################################
 
+class VFwdType final {
+public:
+    enum en : uint8_t { NONE, ENUM, STRUCT, UNION, CLASS, INTERFACE_CLASS };
+    enum en m_e;
+    const char* ascii() const {
+        static const char* const names[]
+            = {"none", "enum", "struct", "union", "class", "interface class"};
+        return names[m_e];
+    }
+    VFwdType()
+        : m_e{NONE} {}
+    // cppcheck-suppress noExplicitConstructor
+    constexpr VFwdType(en _e)
+        : m_e{_e} {}
+    explicit VFwdType(int _e)
+        : m_e(static_cast<en>(_e)) {}  // Need () or GCC 4.8 false warning
+    constexpr operator en() const { return m_e; }
+};
+constexpr bool operator==(const VFwdType& lhs, const VFwdType& rhs) { return lhs.m_e == rhs.m_e; }
+constexpr bool operator==(const VFwdType& lhs, VFwdType::en rhs) { return lhs.m_e == rhs; }
+constexpr bool operator==(VFwdType::en lhs, const VFwdType& rhs) { return lhs == rhs.m_e; }
+inline std::ostream& operator<<(std::ostream& os, const VFwdType& rhs) {
+    return os << rhs.ascii();
+}
+
+// ######################################################################
+
 class VSigning final {
 public:
     enum en : uint8_t {
diff --git a/src/V3AstNodeDType.h b/src/V3AstNodeDType.h
index b27494736..3b4aa1f84 100644
--- a/src/V3AstNodeDType.h
+++ b/src/V3AstNodeDType.h
@@ -1006,12 +1006,14 @@ class AstParamTypeDType final : public AstNodeDType {
     // A parameter type statement; much like a var or typedef
     // @astgen op1 := childDTypep : Optional[AstNodeDType]
     const VVarType m_varType;  // Type of variable (for localparam vs. param)
+    const VFwdType m_fwdType;  // Forward type for lint check
     string m_name;  // Name of variable
 public:
-    AstParamTypeDType(FileLine* fl, VVarType type, const string& name, VFlagChildDType,
-                      AstNodeDType* dtp)
+    AstParamTypeDType(FileLine* fl, VVarType type, VFwdType fwdType, const string& name,
+                      VFlagChildDType, AstNodeDType* dtp)
         : ASTGEN_SUPER_ParamTypeDType(fl)
         , m_varType{type}
+        , m_fwdType{fwdType}
         , m_name{name} {
         childDTypep(dtp);  // Only for parser
         dtypep(nullptr);  // V3Width will resolve
@@ -1036,6 +1038,7 @@ public:
     bool hasDType() const override VL_MT_SAFE { return true; }
     void name(const string& flag) override { m_name = flag; }
     VVarType varType() const { return m_varType; }  // * = Type of variable
+    VFwdType fwdType() const { return m_fwdType; }
     bool isParam() const { return true; }
     bool isGParam() const { return (varType() == VVarType::GPARAM); }
     bool isCompound() const override {
@@ -1047,9 +1050,11 @@ class AstParseTypeDType final : public AstNodeDType {
     // Parents: VAR
     // During parsing, this indicates the type of a parameter is a "parameter type"
     // e.g. the data type is a container of any data type
+    const VFwdType m_fwdType;  // Forward type for lint check
 public:
-    explicit AstParseTypeDType(FileLine* fl)
-        : ASTGEN_SUPER_ParseTypeDType(fl) {}
+    explicit AstParseTypeDType(FileLine* fl, VFwdType fwdType = VFwdType::NONE)
+        : ASTGEN_SUPER_ParseTypeDType(fl)
+        , m_fwdType{fwdType} {}
     ASTGEN_MEMBERS_AstParseTypeDType;
     AstNodeDType* dtypep() const VL_MT_STABLE { return nullptr; }
     // METHODS
@@ -1061,6 +1066,7 @@ public:
         v3fatalSrc("call isCompound on subdata type, not reference");
         return false;
     }
+    VFwdType fwdType() const { return m_fwdType; }
 };
 class AstQueueDType final : public AstNodeDType {
     // Queue array data type, ie "[ $ ]"
diff --git a/src/V3LinkParse.cpp b/src/V3LinkParse.cpp
index 1c650b51e..16050d065 100644
--- a/src/V3LinkParse.cpp
+++ b/src/V3LinkParse.cpp
@@ -322,7 +322,7 @@ class LinkParseVisitor final : public VNVisitor {
             nodep->v3warn(NEWERSTD,
                           "Parameter requires default value, or use IEEE 1800-2009 or later.");
         }
-        if (VN_IS(nodep->subDTypep(), ParseTypeDType)) {
+        if (AstParseTypeDType* const ptypep = VN_CAST(nodep->subDTypep(), ParseTypeDType)) {
             // It's a parameter type. Use a different node type for this.
             AstNode* dtypep = nodep->valuep();
             if (dtypep) {
@@ -331,8 +331,9 @@ class LinkParseVisitor final : public VNVisitor {
                 dtypep = new AstVoidDType{nodep->fileline()};
             }
             AstNode* const newp = new AstParamTypeDType{
-                nodep->fileline(), nodep->varType(), nodep->name(), VFlagChildDType{},
-                new AstRequireDType{nodep->fileline(), dtypep}};
+                nodep->fileline(), nodep->varType(),
+                ptypep->fwdType(), nodep->name(),
+                VFlagChildDType{}, new AstRequireDType{nodep->fileline(), dtypep}};
             nodep->replaceWith(newp);
             VL_DO_DANGLING(nodep->deleteTree(), nodep);
             return;
diff --git a/src/V3Param.cpp b/src/V3Param.cpp
index bfee3e4fe..b0a12f8dd 100644
--- a/src/V3Param.cpp
+++ b/src/V3Param.cpp
@@ -782,6 +782,24 @@ class ParamProcessor final {
                 // Constify may have caused pinp->exprp to change
                 rawTypep = VN_AS(pinp->exprp(), NodeDType);
                 exprp = rawTypep->skipRefToNonRefp();
+                bool ok = true;
+                switch (modvarp->fwdType()) {
+                case VFwdType::NONE: ok = true; break;
+                case VFwdType::ENUM: ok = VN_IS(exprp, EnumDType); break;
+                case VFwdType::STRUCT: ok = VN_IS(exprp, StructDType); break;
+                case VFwdType::UNION: ok = VN_IS(exprp, UnionDType); break;
+                case VFwdType::CLASS: ok = VN_IS(exprp, ClassRefDType); break;
+                case VFwdType::INTERFACE_CLASS:  // TODO: Over permissive for now:
+                    ok = VN_IS(exprp, ClassRefDType);
+                    break;
+                default: modvarp->v3fatalSrc("Bad case");
+                }
+                if (!ok) {
+                    pinp->v3error("Parameter type expression type "
+                                  << exprp->prettyDTypeNameQ()
+                                  << " violates parameter's forwarding type '"
+                                  << modvarp->fwdType().ascii() << "'");
+                }
                 if (exprp->similarDType(origp)) {
                     // Setting parameter to its default value.  Just ignore it.
                     // This prevents making additional modules, and makes coverage more
diff --git a/src/V3ParseImp.h b/src/V3ParseImp.h
index c7895d3f3..9dededfdb 100644
--- a/src/V3ParseImp.h
+++ b/src/V3ParseImp.h
@@ -125,6 +125,7 @@ struct V3ParseBisonYYSType final {
         VAttrType::en attrtypeen;
         VAssertType::en asserttypeen;
         VAssertDirectiveType::en assertdirectivetypeen;
+        VFwdType::en fwdtype;
         VLifetime::en lifetime;
         VStrength::en strength;
 
diff --git a/src/verilog.y b/src/verilog.y
index 74c322350..3e4ed1251 100644
--- a/src/verilog.y
+++ b/src/verilog.y
@@ -1916,9 +1916,11 @@ parameter_declarationFront:     // IEEE: local_ or parameter_declaration w/o ass
 
 parameter_declarationTypeFront: // IEEE: local_ or parameter_declaration w/o assignment
         //                      // Front must execute first so VARDTYPE is ready before list of vars
-                varParamReset yTYPE__ETC                { /*VARRESET-in-varParam*/ VARDTYPE(new AstParseTypeDType{$2}); }
-        |       varParamReset yTYPE__ETC forward_type   { /*VARRESET-in-varParam*/ VARDTYPE(new AstParseTypeDType{$2});
-                                                          BBUNSUP($<fl>1, "Unsupported: 'parameter type' forward type"); }
+                varParamReset yTYPE__ETC
+                        { /*VARRESET-in-varParam*/ VARDTYPE(new AstParseTypeDType{$2}); }
+        |       varParamReset yTYPE__ETC forward_type
+                        { /*VARRESET-in-varParam*/
+                          AstNodeDType* const dtp = new AstParseTypeDType{$2, $3}; VARDTYPE(dtp); }
         ;
 
 parameter_port_declarationFrontE: // IEEE: local_ or parameter_port_declaration w/o assignment
@@ -1939,20 +1941,26 @@ parameter_port_declarationTypeFrontE: // IEEE: parameter_port_declaration w/o as
         //                      // IEEE: parameter_declaration (minus assignment)
         //                      // IEEE: local_parameter_declaration (minus assignment)
         //                      // Front must execute first so VARDTYPE is ready before list of vars
-                varParamReset yTYPE__ETC                { /*VARRESET-in-varParam*/ VARDTYPE(new AstParseTypeDType{$2}); }
-        |       varParamReset yTYPE__ETC forward_type   { /*VARRESET-in-varParam*/ VARDTYPE(new AstParseTypeDType{$2});
-                                                          BBUNSUP($<fl>1, "Unsupported: 'parameter type' forward type"); }
-        |       yTYPE__ETC                              { /*VARRESET-in-varParam*/ VARDTYPE(new AstParseTypeDType{$1}); }
-        |       yTYPE__ETC forward_type                 { /*VARRESET-in-varParam*/ VARDTYPE(new AstParseTypeDType{$1});
-                                                          BBUNSUP($<fl>1, "Unsupported: 'parameter type' forward type"); }
+                varParamReset yTYPE__ETC
+                        { /*VARRESET-in-varParam*/
+                          AstNodeDType* const dtp = new AstParseTypeDType{$2}; VARDTYPE(dtp); }
+        |       varParamReset yTYPE__ETC forward_type
+                        { /*VARRESET-in-varParam*/
+                          AstNodeDType* const dtp = new AstParseTypeDType{$2, $3}; VARDTYPE(dtp); }
+        |       yTYPE__ETC
+                        { /*VARRESET-in-varParam*/
+                          AstNodeDType* const dtp = new AstParseTypeDType{$1}; VARDTYPE(dtp); }
+        |       yTYPE__ETC forward_type
+                        { /*VARRESET-in-varParam*/
+                          AstNodeDType* const dtp = new AstParseTypeDType{$1, $2}; VARDTYPE(dtp); }
         ;
 
-forward_type:  // ==IEEE: forward_type
-                yENUM                                   { }
-        |       ySTRUCT                                 { }
-        |       yUNION                                  { }
-        |       yCLASS                                  { }
-        |       yINTERFACE yCLASS                       { }
+forward_type<fwdtype>:  // ==IEEE: forward_type
+                yENUM                                   { $$ = VFwdType::ENUM; }
+        |       ySTRUCT                                 { $$ = VFwdType::STRUCT; }
+        |       yUNION                                  { $$ = VFwdType::UNION; }
+        |       yCLASS                                  { $$ = VFwdType::CLASS; }
+        |       yINTERFACE yCLASS                       { $$ = VFwdType::INTERFACE_CLASS; }
         ;
 
 net_declaration<nodep>:         // IEEE: net_declaration - excluding implict
diff --git a/test_regress/t/t_concat_string.py b/test_regress/t/t_concat_string.py
index 2b17673d7..262a0d4b4 100755
--- a/test_regress/t/t_concat_string.py
+++ b/test_regress/t/t_concat_string.py
@@ -12,7 +12,7 @@ import vltest_bootstrap
 
 test.scenarios('simulator')
 
-signal.alarm(5)  # 5s timeout
+signal.alarm(15)  # 15s timeout
 
 test.compile()
 
diff --git a/test_regress/t/t_param_type_fwd.out b/test_regress/t/t_param_type_fwd.out
deleted file mode 100644
index e2b38098f..000000000
--- a/test_regress/t/t_param_type_fwd.out
+++ /dev/null
@@ -1,32 +0,0 @@
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:10:4: Unsupported: 'parameter type' forward type
-   10 |    parameter type enum E_t;
-      |    ^~~~~~~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:11:4: Unsupported: 'parameter type' forward type
-   11 |    parameter type struct S_t;
-      |    ^~~~~~~~~
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:12:4: Unsupported: 'parameter type' forward type
-   12 |    parameter type union U_t;
-      |    ^~~~~~~~~
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:13:4: Unsupported: 'parameter type' forward type
-   13 |    parameter type class C_t;
-      |    ^~~~~~~~~
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:14:4: Unsupported: 'parameter type' forward type
-   14 |    parameter type interface class IC_t;
-      |    ^~~~~~~~~
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:17:13: Unsupported: 'parameter type' forward type
-   17 | class Cls #(parameter type enum E_t,
-      |             ^~~~~~~~~
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:18:13: Unsupported: 'parameter type' forward type
-   18 |             parameter type struct S_t,
-      |             ^~~~~~~~~
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:19:13: Unsupported: 'parameter type' forward type
-   19 |             parameter type union U_t,
-      |             ^~~~~~~~~
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:20:13: Unsupported: 'parameter type' forward type
-   20 |             parameter type class C_t,
-      |             ^~~~~~~~~
-%Error-UNSUPPORTED: t/t_param_type_fwd.v:21:13: Unsupported: 'parameter type' forward type
-   21 |             parameter type interface class IC_t);
-      |             ^~~~~~~~~
-%Error: Exiting due to
diff --git a/test_regress/t/t_param_type_fwd.py b/test_regress/t/t_param_type_fwd.py
index e33e10acf..f81c3d68d 100755
--- a/test_regress/t/t_param_type_fwd.py
+++ b/test_regress/t/t_param_type_fwd.py
@@ -11,6 +11,6 @@ import vltest_bootstrap
 
 test.scenarios('vlt')
 
-test.lint(fails=True, expect_filename=test.golden_filename)
+test.lint()
 
 test.passes()
diff --git a/test_regress/t/t_param_type_fwd.v b/test_regress/t/t_param_type_fwd.v
index 375495398..f84a2d567 100644
--- a/test_regress/t/t_param_type_fwd.v
+++ b/test_regress/t/t_param_type_fwd.v
@@ -4,9 +4,19 @@
 // without warranty, 2024 by Wilson Snyder.
 // SPDX-License-Identifier: CC0-1.0
 
-// Test for trace file interface aliasing
+typedef enum { ONE } e_t;
 
-module m;
+typedef struct { int m_i; } s_t;
+
+typedef union { int m_i; } u_t;
+
+class c_t;
+endclass
+
+interface class ic_t;
+endclass
+
+module sub;
    parameter type enum E_t;
    parameter type struct S_t;
    parameter type union U_t;
@@ -21,6 +31,10 @@ class Cls #(parameter type enum E_t,
             parameter type interface class IC_t);
 endclass
 
-module t (/*AUTOARG*/);
-   // TODO proper test
+module t;
+   sub #(.E_t(e_t), .S_t(s_t), .U_t(u_t), .C_t(c_t), .IC_t(ic_t)) sub();
+   Cls #(.E_t(e_t), .S_t(s_t), .U_t(u_t), .C_t(c_t), .IC_t(ic_t)) c;
+   initial begin
+      c = new;
+   end
 endmodule
diff --git a/test_regress/t/t_param_type_fwd_bad.out b/test_regress/t/t_param_type_fwd_bad.out
new file mode 100644
index 000000000..42da02e1f
--- /dev/null
+++ b/test_regress/t/t_param_type_fwd_bad.out
@@ -0,0 +1,42 @@
+%Error: t/t_param_type_fwd_bad.v:25:11: Parameter type expression type 'int' violates parameter's forwarding type 'enum'
+                                      : ... note: In instance 't'
+   25 |    sub #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) sub();
+      |           ^~~
+        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
+%Error: t/t_param_type_fwd_bad.v:25:24: Parameter type expression type 'int' violates parameter's forwarding type 'struct'
+                                      : ... note: In instance 't'
+   25 |    sub #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) sub();
+      |                        ^~~
+%Error: t/t_param_type_fwd_bad.v:25:37: Parameter type expression type 'int' violates parameter's forwarding type 'union'
+                                      : ... note: In instance 't'
+   25 |    sub #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) sub();
+      |                                     ^~~
+%Error: t/t_param_type_fwd_bad.v:25:50: Parameter type expression type 'int' violates parameter's forwarding type 'class'
+                                      : ... note: In instance 't'
+   25 |    sub #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) sub();
+      |                                                  ^~~
+%Error: t/t_param_type_fwd_bad.v:25:63: Parameter type expression type 'int' violates parameter's forwarding type 'interface class'
+                                      : ... note: In instance 't'
+   25 |    sub #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) sub();
+      |                                                               ^~~~
+%Error: t/t_param_type_fwd_bad.v:26:11: Parameter type expression type 'int' violates parameter's forwarding type 'enum'
+                                      : ... note: In instance 't'
+   26 |    Cls #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) c;
+      |           ^~~
+%Error: t/t_param_type_fwd_bad.v:26:24: Parameter type expression type 'int' violates parameter's forwarding type 'struct'
+                                      : ... note: In instance 't'
+   26 |    Cls #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) c;
+      |                        ^~~
+%Error: t/t_param_type_fwd_bad.v:26:37: Parameter type expression type 'int' violates parameter's forwarding type 'union'
+                                      : ... note: In instance 't'
+   26 |    Cls #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) c;
+      |                                     ^~~
+%Error: t/t_param_type_fwd_bad.v:26:50: Parameter type expression type 'int' violates parameter's forwarding type 'class'
+                                      : ... note: In instance 't'
+   26 |    Cls #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) c;
+      |                                                  ^~~
+%Error: t/t_param_type_fwd_bad.v:26:63: Parameter type expression type 'int' violates parameter's forwarding type 'interface class'
+                                      : ... note: In instance 't'
+   26 |    Cls #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) c;
+      |                                                               ^~~~
+%Error: Exiting due to
diff --git a/test_regress/t/t_param_type_fwd_bad.py b/test_regress/t/t_param_type_fwd_bad.py
new file mode 100755
index 000000000..e33e10acf
--- /dev/null
+++ b/test_regress/t/t_param_type_fwd_bad.py
@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('vlt')
+
+test.lint(fails=True, expect_filename=test.golden_filename)
+
+test.passes()
diff --git a/test_regress/t/t_param_type_fwd_bad.v b/test_regress/t/t_param_type_fwd_bad.v
new file mode 100644
index 000000000..5a9e1820f
--- /dev/null
+++ b/test_regress/t/t_param_type_fwd_bad.v
@@ -0,0 +1,30 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2025 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+typedef int int_t;
+
+module sub;
+   parameter type enum E_t;
+   parameter type struct S_t;
+   parameter type union U_t;
+   parameter type class C_t;
+   parameter type interface class IC_t;
+endmodule
+
+class Cls #(parameter type enum E_t,
+            parameter type struct S_t,
+            parameter type union U_t,
+            parameter type class C_t,
+            parameter type interface class IC_t);
+endclass
+
+module t (/*AUTOARG*/);
+   sub #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) sub();
+   Cls #(.E_t(int_t), .S_t(int_t), .U_t(int_t), .C_t(int_t), .IC_t(int_t)) c;
+   initial begin
+      c = new;
+   end
+endmodule