diff --git a/Changes b/Changes
index 49c934b1c..1e63f4b07 100644
--- a/Changes
+++ b/Changes
@@ -27,7 +27,7 @@ The contributors that suggested a given feature are shown in []. Thanks!
 ****  Fix multithreaded yield behavior when no work.  [Patrick Stewart]
 
 ****  Fix bad-syntax crashes, bug1548, bug1550-1553, bug1557-1560, bug1563,
-      bug1573-1577, bug1582-1585. [Eric Rippey]
+      bug1573-1577, bug1582-1585, bug1591. [Eric Rippey]
 
 ****  Fix false CMPCONST/UNSIGNED warnings on "inside", bug1581. [Mitch Hayenga]
 
diff --git a/src/V3Simulate.h b/src/V3Simulate.h
index e77878ba4..86601475f 100644
--- a/src/V3Simulate.h
+++ b/src/V3Simulate.h
@@ -396,7 +396,7 @@ private:
                     clearOptimizable(nodep, "Var write & read");
                 }
                 vscp->user1( vscp->user1() | VU_RV);
-                bool isConst = nodep->varp()->isParam();
+                bool isConst = nodep->varp()->isParam() && nodep->varp()->valuep();
                 AstConst* constp = isConst ? fetchConstNull(nodep->varp()->valuep()) : NULL;
                 if (isConst && constp) {  // Propagate PARAM constants for constant function analysis
                     if (!m_checkOnly && optimizable()) {
diff --git a/src/V3Width.cpp b/src/V3Width.cpp
index cd7e5bbc0..94044c01a 100644
--- a/src/V3Width.cpp
+++ b/src/V3Width.cpp
@@ -952,6 +952,7 @@ private:
         AstAttrOf* oldAttr = m_attrp;
         m_attrp = nodep;
         userIterateAndNext(nodep->fromp(), WidthVP(SELF, BOTH).p());
+        if (nodep->dimp()) userIterateAndNext(nodep->dimp(), WidthVP(SELF, BOTH).p());
         // Don't iterate children, don't want to lose VarRef.
         switch (nodep->attrType()) {
         case AstAttrType::VAR_BASE:
@@ -981,9 +982,13 @@ private:
                         "Unsized expression");
             std::pair<uint32_t,uint32_t> dim
                 = nodep->fromp()->dtypep()->skipRefp()->dimensions(true);
-            uint32_t msbdim = dim.first+dim.second;
-            if (!nodep->dimp() || VN_IS(nodep->dimp(), Const) || msbdim<1) {
-                int dim = !nodep->dimp() ? 1 : VN_CAST(nodep->dimp(), Const)->toSInt();
+            uint32_t msbdim = dim.first + dim.second;
+            if (!nodep->dimp() || msbdim < 1) {
+                int dim = 1;
+                AstConst* newp = dimensionValue(nodep->fromp()->dtypep(), nodep->attrType(), dim);
+                nodep->replaceWith(newp); nodep->deleteTree(); VL_DANGLING(nodep);
+            } else if (VN_IS(nodep->dimp(), Const)) {
+                int dim = VN_CAST(nodep->dimp(), Const)->toSInt();
                 AstConst* newp = dimensionValue(nodep->fromp()->dtypep(), nodep->attrType(), dim);
                 nodep->replaceWith(newp); nodep->deleteTree(); VL_DANGLING(nodep);
             }
diff --git a/test_regress/t/t_param_noval_bad.out b/test_regress/t/t_param_noval_bad.out
new file mode 100644
index 000000000..054055470
--- /dev/null
+++ b/test_regress/t/t_param_noval_bad.out
@@ -0,0 +1,29 @@
+%Error: t/t_param_noval_bad.v:6: Parameter without initial value is never given value (IEEE 1800-2017 6.20.1): 'P'
+                               : ... In instance t
+module t #(parameter P);
+                     ^
+%Warning-WIDTH: t/t_param_noval_bad.v:9: Logical Operator GENFOR expects 1 bit on the For Test Condition, but For Test Condition's VARREF 'P' generates 32 bits.
+                                       : ... In instance t
+      for (j=0; P; j++)
+      ^~~
+                ... Use "/* verilator lint_off WIDTH */" and lint_on around source to disable this message.
+%Error: t/t_param_noval_bad.v:9: Non-genvar used in generate for: 'j'
+                               : ... In instance t
+      for (j=0; P; j++)
+      ^~~
+%Error: t/t_param_noval_bad.v:9: Loop unrolling failed.
+                               : ... In instance t
+      for (j=0; P; j++)
+      ^~~
+%Error: t/t_param_noval_bad.v:9: Unsupported: Can't unroll generate for; Unable to unroll loop
+                               : ... In instance t
+      for (j=0; P; j++)
+      ^~~
+%Error: t/t_param_noval_bad.v:9: For loop doesn't have genvar index, or is malformed
+                               : ... In instance t
+      for (j=0; P; j++)
+      ^~~
+%Error: Internal Error: t/t_param_noval_bad.v:9: ../V3Param.cpp:505: GENFOR should have been wrapped in BEGIN
+                                               : ... In instance t
+      for (j=0; P; j++)
+      ^~~
diff --git a/test_regress/t/t_param_noval_bad.pl b/test_regress/t/t_param_noval_bad.pl
new file mode 100755
index 000000000..573f98f12
--- /dev/null
+++ b/test_regress/t/t_param_noval_bad.pl
@@ -0,0 +1,18 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2008 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.
+
+scenarios(linter => 1);
+
+lint(
+    fails => 1,
+    expect_filename => $Self->{golden_filename},
+    );
+
+ok(1);
+1;
diff --git a/test_regress/t/t_param_noval_bad.v b/test_regress/t/t_param_noval_bad.v
new file mode 100644
index 000000000..9575ca824
--- /dev/null
+++ b/test_regress/t/t_param_noval_bad.v
@@ -0,0 +1,12 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2019 by Wilson Snyder.
+
+module t #(parameter P);
+   generate
+      var j;
+      for (j=0; P; j++)
+        initial begin end
+   endgenerate
+endmodule