diff --git a/Changes b/Changes
index 98e5eda6e..999fe55e6 100644
--- a/Changes
+++ b/Changes
@@ -21,6 +21,7 @@ Verilator 5.041 devel
 * Add $(LDFLAGS) and $(LIBS) to when building shared libraries (#6425) (#6426). [Ahmed El-Mahmoudy]
 * Add ASSIGNEQEXPR when use `=` inside expressions (#5567). [Ethan Sifferman]
 * Add IMPLICITSTATIC also on procedure variables.
+* Add error on function invoking task.
 * Deprecate sensitivity list on public_flat_rw attributes (#6443). [Geza Lore]
 * Deprecate clocker attribute and --clk option (#6463). [Geza Lore]
 * Support modports referencing clocking blocks (#4555) (#6436). [Ryszard Rozak, Antmicro Ltd.]
diff --git a/src/V3AstNodeOther.h b/src/V3AstNodeOther.h
index d7d707d56..04fdc630c 100644
--- a/src/V3AstNodeOther.h
+++ b/src/V3AstNodeOther.h
@@ -132,6 +132,8 @@ class AstNodeFTask VL_NOT_FINAL : public AstNode {
     bool m_recursive : 1;  // Recursive or part of recursion
     bool m_static : 1;  // Static method in class
     bool m_underGenerate : 1;  // Under generate (for warning)
+    bool m_verilogFunction : 1;  // Declared by user as function (versus internal-made)
+    bool m_verilogTask : 1;  // Declared by user as task (versus internal-made)
     bool m_virtual : 1;  // Virtual method in class
     bool m_needProcess : 1;  // Needs access to VlProcess of the caller
     VBaseOverride m_baseOverride;  // BaseOverride (inital/final/extends)
@@ -162,6 +164,8 @@ protected:
         , m_recursive{false}
         , m_static{false}
         , m_underGenerate{false}
+        , m_verilogFunction{false}
+        , m_verilogTask{false}
         , m_virtual{false}
         , m_needProcess{false} {
         addStmtsp(stmtsp);
@@ -227,6 +231,10 @@ public:
     void isStatic(bool flag) { m_static = flag; }
     bool underGenerate() const { return m_underGenerate; }
     void underGenerate(bool flag) { m_underGenerate = flag; }
+    bool verilogFunction() const { return m_verilogFunction; }
+    void verilogFunction(bool flag) { m_verilogFunction = flag; }
+    bool verilogTask() const { return m_verilogTask; }
+    void verilogTask(bool flag) { m_verilogTask = flag; }
     bool isVirtual() const { return m_virtual; }
     void isVirtual(bool flag) { m_virtual = flag; }
     bool needProcess() const { return m_needProcess; }
diff --git a/src/V3AstNodes.cpp b/src/V3AstNodes.cpp
index 9e85e993c..a73ff7c01 100644
--- a/src/V3AstNodes.cpp
+++ b/src/V3AstNodes.cpp
@@ -2901,6 +2901,8 @@ void AstNodeFTask::dump(std::ostream& str) const {
     if (recursive()) str << " [RECURSIVE]";
     if (taskPublic()) str << " [PUBLIC]";
     if (isStatic()) str << " [STATIC]";
+    if (verilogTask()) str << " [VTASK]";
+    if (verilogFunction()) str << " [VFUNC]";
     if ((dpiImport() || dpiExport()) && cname() != name()) str << " [c=" << cname() << "]";
 }
 bool AstNodeFTask::isPure() {
diff --git a/src/V3WidthCommit.cpp b/src/V3WidthCommit.cpp
index bc75e3e0d..00cf1f659 100644
--- a/src/V3WidthCommit.cpp
+++ b/src/V3WidthCommit.cpp
@@ -45,11 +45,13 @@ class WidthCommitVisitor final : public VNVisitor {
     const VNUser2InUse m_inuser2;
 
     // STATE
-    AstNodeModule* m_modp = nullptr;
+    AstNodeFTask* m_ftaskp = nullptr;  // Current function/task
+    AstNodeModule* m_modp = nullptr;  // Current module
     std::string m_contNba;  // In continuous- or non-blocking assignment
     bool m_dynsizedelem
         = false;  // Writing a dynamically-sized array element, not the array itself
     VMemberMap m_memberMap;  // Member names cached for fast lookup
+    bool m_taskRefWarn = true;  // Allow task reference warnings
     bool m_underSel = false;  // Under AstMemberSel or AstSel
     bool m_underAlwaysClocked = false;  // Under always with sequential SenTree
     std::vector<AstNew*> m_virtualNewsp;  // Instantiations of virtual classes
@@ -216,6 +218,13 @@ private:
         iterateChildren(nodep);
         editDType(nodep);
     }
+    void visit(AstFork* nodep) override {
+        VL_RESTORER(m_taskRefWarn);
+        // fork..join_any is allowed to call tasks, and UVM does this
+        if (nodep->joinType().joinNone()) m_taskRefWarn = false;
+        iterateChildren(nodep);
+        editDType(nodep);
+    }
     void visit(AstSenTree* nodep) override {
         if (nodep->sensesp() && nodep->sensesp()->isComboStar()) {
             UASSERT_OBJ(!nodep->sensesp()->nextp(), nodep, "Shouldn't be senitems after .*");
@@ -317,6 +326,8 @@ private:
     void visit(AstNodeFTask* nodep) override {
         if (!nodep->taskPublic() && !nodep->dpiExport() && !nodep->dpiImport())
             m_tasksp.push_back(nodep);
+        VL_RESTORER(m_ftaskp);
+        m_ftaskp = nodep;
         iterateChildren(nodep);
         editDType(nodep);
         {
@@ -419,6 +430,17 @@ private:
         iterateChildren(nodep);
         editDType(nodep);
         classEncapCheck(nodep, nodep->taskp(), VN_CAST(nodep->classOrPackagep(), Class));
+        if (nodep->taskp() && nodep->taskp()->verilogTask() && m_ftaskp
+            && m_ftaskp->verilogFunction() && m_taskRefWarn) {
+            nodep->v3error("Functions cannot invoke tasks (IEEE 1800-2023 13.4)\n"
+                           << nodep->warnContextPrimary() << "\n"
+                           << nodep->warnMore() << "... Suggest make caller 'function "
+                           << m_ftaskp->prettyName() << "' a task\n"
+                           << m_ftaskp->warnContextSecondary() << "\n"
+                           << nodep->warnMore() << "... Or, suggest make called 'task "
+                           << nodep->taskp()->prettyName() << "' a function void\n"
+                           << nodep->taskp()->warnContextSecondary());
+        }
         if (nodep->taskp()) nodep->taskp()->user2(1);
         if (AstNew* const newp = VN_CAST(nodep, New)) {
             if (!VN_IS(newp->backp(), Assign)) return;
diff --git a/src/verilog.y b/src/verilog.y
index 96290e020..1fe51788c 100644
--- a/src/verilog.y
+++ b/src/verilog.y
@@ -4546,14 +4546,17 @@ lifetime<lifetime>:             // ==IEEE: lifetime
 
 taskId<nodeFTaskp>:
                 id
-                        { $$ = new AstTask{$<fl>$, *$1, nullptr}; }
+                        { $$ = new AstTask{$<fl>$, *$1, nullptr};
+                          $$->verilogTask(true); }
         //
         |       id/*interface_identifier*/ '.' idAny
                         { $$ = new AstTask{$<fl>$, *$3, nullptr};
+                          $$->verilogTask(true);
                           BBUNSUP($2, "Unsupported: Out of block function declaration"); }
         //
         |       packageClassScope id
                         { $$ = new AstTask{$<fl>$, *$2, nullptr};
+                          $$->verilogTask(true);
                           $$->classOrPackagep($1);
                           $$->classMethod(true); }
         ;
@@ -4584,18 +4587,23 @@ funcId<nodeFTaskp>:             // IEEE: function_data_type_or_implicit + part o
                           $$->fvarp(GRAMMARP->createArray(refp, $4, true)); }
         //                      // To verilator tasks are the same as void functions (we separately detect time passing)
         |       yVOID taskId
-                        { $$ = $2; }
+                        { $$ = $2;  // Internals represent it as a task, not a function (TODO cleanup)
+                          $$->verilogTask(false);
+                          $$->verilogFunction(true); }
         ;
 
 funcIdNew<nodeFTaskp>:          // IEEE: from class_constructor_declaration
                 yNEW__ETC
                         { $$ = new AstFunc{$<fl>1, "new", nullptr, nullptr};
+                          $$->verilogFunction(true);
                           $$->isConstructor(true); }
         |       yNEW__PAREN
                         { $$ = new AstFunc{$<fl>1, "new", nullptr, nullptr};
+                          $$->verilogFunction(true);
                           $$->isConstructor(true); }
         |       packageClassScopeNoId yNEW__PAREN
                         { $$ = new AstFunc{$<fl>2, "new", nullptr, nullptr};
+                          $$->verilogFunction(true);
                           $$->classOrPackagep($1);
                           $$->isConstructor(true);
                           $$->classMethod(true); }
@@ -4605,16 +4613,19 @@ fIdScoped<funcp>:               // IEEE: part of function_body_declaration/task_
         //                      // IEEE: [ interface_identifier '.' | class_scope ] function_identifier
                 id
                         { $<fl>$ = $<fl>1;
-                          $$ = new AstFunc{$<fl>$, *$1, nullptr, nullptr}; }
+                          $$ = new AstFunc{$<fl>$, *$1, nullptr, nullptr};
+                          $$->verilogFunction(true); }
         //
         |       id/*interface_identifier*/ '.' idAny
                         { $<fl>$ = $<fl>1;
                           $$ = new AstFunc{$<fl>$, *$1, nullptr, nullptr};
+                          $$->verilogFunction(true);
                           BBUNSUP($2, "Unsupported: Out of block function declaration"); }
         //
         |       packageClassScope id
                         { $<fl>$ = $<fl>1;
                           $$ = new AstFunc{$<fl>$, *$2, nullptr, nullptr};
+                          $$->verilogFunction(true);
                           $$->classMethod(true);
                           $$->classOrPackagep($1); }
         ;
diff --git a/test_regress/t/t_func_task_bad.out b/test_regress/t/t_func_task_bad.out
index 2cb9809f4..3d3dbfb9a 100644
--- a/test_regress/t/t_func_task_bad.out
+++ b/test_regress/t/t_func_task_bad.out
@@ -1,10 +1,10 @@
-%Error: t/t_func_task_bad.v:10:11: Cannot call a task/void-function as a function: 'task_as_func'
-                                 : ... note: In instance 't'
-   10 |       if (task_as_func(1'b0)) $stop;
-      |           ^~~~~~~~~~~~
-        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
-%Error: t/t_func_task_bad.v:10:7: Logical operator IF expects a non-complex data type on the If.
+%Error: t/t_func_task_bad.v:10:9: Cannot call a task/void-function as a function: 'a_task'
                                 : ... note: In instance 't'
-   10 |       if (task_as_func(1'b0)) $stop;
-      |       ^~
+   10 |     if (a_task(1'b0)) $stop;   
+      |         ^~~~~~
+        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
+%Error: t/t_func_task_bad.v:10:5: Logical operator IF expects a non-complex data type on the If.
+                                : ... note: In instance 't'
+   10 |     if (a_task(1'b0)) $stop;   
+      |     ^~
 %Error: Exiting due to
diff --git a/test_regress/t/t_func_task_bad.v b/test_regress/t/t_func_task_bad.v
index dcf2f685d..9f0e668b3 100644
--- a/test_regress/t/t_func_task_bad.v
+++ b/test_regress/t/t_func_task_bad.v
@@ -6,12 +6,12 @@
 
 module t;
 
-   initial begin
-      if (task_as_func(1'b0)) $stop;
-   end
+  initial begin
+    if (a_task(1'b0)) $stop;  // <--- Bad: Calling task _as_ function
+  end
 
-   task task_as_func;
-      input ign;
-   endtask
+  task a_task;
+    input ign;
+  endtask
 
 endmodule
diff --git a/test_regress/t/t_func_task_bad2.out b/test_regress/t/t_func_task_bad2.out
new file mode 100644
index 000000000..174c5e0f4
--- /dev/null
+++ b/test_regress/t/t_func_task_bad2.out
@@ -0,0 +1,12 @@
+%Error: t/t_func_task_bad2.v:14:5: Functions cannot invoke tasks (IEEE 1800-2023 13.4)
+                                 : ... note: In instance 't'
+   14 |     a_task(1'b0);   
+      |     ^~~~~~
+                                 : ... Suggest make caller 'function func_calls_task' a task
+   13 |   function void func_calls_task;
+      |                 ^~~~~~~~~~~~~~~
+                                 : ... Or, suggest make called 'task a_task' a function void
+    9 |   task a_task;
+      |        ^~~~~~
+        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
+%Error: Exiting due to
diff --git a/test_regress/t/t_func_task_bad2.py b/test_regress/t/t_func_task_bad2.py
new file mode 100755
index 000000000..5df24a780
--- /dev/null
+++ b/test_regress/t/t_func_task_bad2.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('linter')
+
+test.lint(verilator_flags2=['--timing'], fails=True, expect_filename=test.golden_filename)
+
+test.passes()
diff --git a/test_regress/t/t_func_task_bad2.v b/test_regress/t/t_func_task_bad2.v
new file mode 100644
index 000000000..61d06bfe6
--- /dev/null
+++ b/test_regress/t/t_func_task_bad2.v
@@ -0,0 +1,23 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2011 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+
+  task a_task;
+    input ign;
+  endtask
+
+  function void func_calls_task;
+    a_task(1'b0);  // <--- Bad: Calling task _from_ function
+  endfunction
+
+  function void func_ok;
+    fork
+      a_task(1'b0);  // ok, and done in UVM
+    join_none
+  endfunction
+
+endmodule
diff --git a/test_regress/t/t_opt_dead_task.v b/test_regress/t/t_opt_dead_task.v
index fe9e1aeba..cf9f77a6d 100644
--- a/test_regress/t/t_opt_dead_task.v
+++ b/test_regress/t/t_opt_dead_task.v
@@ -4,39 +4,41 @@
 // any use, without warranty, 2025 by Antmicro.
 // SPDX-License-Identifier: CC0-1.0
 
-module t (input clk);
-   // AstLet and AstProperty are also NodeFTasks, but lets are substituted earlier and properties should be "used" by their asserts so also not deadified
-   let nclk = ~clk;
-   assert property(@(posedge clk)1);
+module t (
+    input clk
+);
+  // AstLet and AstProperty are also NodeFTasks, but lets are substituted earlier and properties should be "used" by their asserts so also not deadified
+  let nclk = ~clk;
+  assert property (@(posedge clk) 1);
 
-   function void livefunc();
-   endfunction
-   task livetask;
-   endtask
-   // Tasks/functions that are called somewhere will not be deadified
-   initial begin
-      livefunc();
-      livetask();
-      $finish;
-   end
+  function void livefunc();
+  endfunction
+  task livetask;
+  endtask
+  // Tasks/functions that are called somewhere will not be deadified
+  initial begin
+    livefunc();
+    livetask();
+    $finish;
+  end
 
-   // These should be deadified
-   function deadfunc();
-      deeptask2();
-   endfunction
-   task deadtask;
-      deeptask1();
-   endtask
-   // A chain of dead tasks calling each other to ensure V3Dead can remove chained dead tasks
-   task deeptask1;
-      deeptask2();
-   endtask
-   task deeptask2;
-      deeptask3();
-   endtask
-   task deeptask3;
-      deeptask4();
-   endtask
-   task deeptask4;
-   endtask
+  // These should be deadified
+  task deadfunc();
+    deeptask2();
+  endtask
+  task deadtask;
+    deeptask1();
+  endtask
+  // A chain of dead tasks calling each other to ensure V3Dead can remove chained dead tasks
+  task deeptask1;
+    deeptask2();
+  endtask
+  task deeptask2;
+    deeptask3();
+  endtask
+  task deeptask3;
+    deeptask4();
+  endtask
+  task deeptask4;
+  endtask
 endmodule
diff --git a/test_regress/t/t_var_in_fork.v b/test_regress/t/t_var_in_fork.v
index 9aaa3f3c7..d4a10079e 100644
--- a/test_regress/t/t_var_in_fork.v
+++ b/test_regress/t/t_var_in_fork.v
@@ -14,7 +14,7 @@ module t();
 
 
   class Foo;
-    function void do_something(int captured_var);
+    task do_something(int captured_var);
       fork
         begin
           int my_var;
@@ -23,7 +23,7 @@ module t();
           my_other_var = captured_var; /* Capture the same value "twice" */
           my_var++;
           static_var++; /* Write to a value with static lifetime (valid) */
-          $display("Vars in forked process: %d %d", my_var, my_other_var);
+          $display("Vars in forked process: %0d %0d", my_var, my_other_var);
           if (my_var != 2)
             $stop;
           if (my_other_var != 1)
@@ -32,7 +32,7 @@ module t();
         end
       join_none
       $display("Leaving fork's parent");
-    endfunction
+    endtask
   endclass
 
   initial begin
@@ -44,14 +44,14 @@ module t();
   end
 
   always @(evt) begin
-    $display("Static variable: %d", static_var);
+    $display("Static variable: %0d", static_var);
     if (static_var != 1)
       $stop;
     fork
       begin
           automatic int my_auto_var = 0;
           my_auto_var++;
-          $display("Automatic variable in fork: %d", my_auto_var);
+          $display("Automatic variable in fork: %0d", my_auto_var);
           if (my_auto_var != 1) $stop;
       end
     join_none