diff --git a/src/V3Const.cpp b/src/V3Const.cpp
index a9c273918..a3c16f85d 100644
--- a/src/V3Const.cpp
+++ b/src/V3Const.cpp
@@ -313,15 +313,24 @@ private:
 	    if (m_warn
 		&& nodep->lsbp()->castConst()
 		&& nodep->widthp()->castConst()
-		&& (!varp->rangep() || varp->msb())  // else it's non-resolvable parameterized
-		&& ( (  (nodep->msbConst() > varp->msbMaxSelect())
-			|| (nodep->lsbConst() > varp->msbMaxSelect())))) {
-		// See also warning in V3Width
-		nodep->v3error("Selection index out of range: "
-			       <<nodep->msbConst()<<":"<<nodep->lsbConst()
-			       <<" outside "<<varp->msbMaxSelect()<<":0"
-			       <<(varp->lsb()>=0 ? ""
-				  :" (adjusted +"+cvtToStr(-varp->lsb())+" to account for negative lsb)"));
+		&& (!varp->rangep() || varp->msb())) {  // else it's non-resolvable parameterized
+		if (nodep->lsbp()->castConst()->num().isFourState()
+		    || nodep->widthp()->castConst()->num().isFourState()) {
+		    nodep->v3error("Selection index is constantly unknown or tristated: "
+				   "lsb="<<nodep->lsbp()->name()<<" width="<<nodep->widthp()->name());
+		    // Replacing nodep will make a mess above, so we replace the offender
+		    replaceZero(nodep->lsbp());
+		}
+		else if ((nodep->msbConst() > varp->msbMaxSelect())
+			 || (nodep->lsbConst() > varp->msbMaxSelect())) {
+		    // See also warning in V3Width
+		    nodep->v3error("Selection index out of range: "
+				   <<nodep->msbConst()<<":"<<nodep->lsbConst()
+				   <<" outside "<<varp->msbMaxSelect()<<":0"
+				   <<(varp->lsb()>=0 ? ""
+				      :" (adjusted +"+cvtToStr(-varp->lsb())+" to account for negative lsb)"));
+		    // Don't replace with zero, we'll do it later
+		}
 	    }
 	}
 	return false;  // Not a transform, so NOP
@@ -367,7 +376,9 @@ private:
     void replaceNum (AstNode* oldp, const V3Number& num) {
 	// Replace oldp node with a constant set to specified value
 	UASSERT (oldp, "Null old\n");
-	if (oldp->castConst()) oldp->v3fatalSrc("Already constant??\n");
+	if (oldp->castConst() && !oldp->castConst()->num().isFourState()) {
+	    oldp->v3fatalSrc("Already constant??\n");
+	}
 	AstNode* newp = new AstConst(oldp->fileline(), num);
 	newp->widthSignedFrom(oldp);
 	if (debug()>5) oldp->dumpTree(cout,"  const_old: ");
diff --git a/test_regress/t/t_select_bad_tri.pl b/test_regress/t/t_select_bad_tri.pl
new file mode 100755
index 000000000..1dd538e88
--- /dev/null
+++ b/test_regress/t/t_select_bad_tri.pl
@@ -0,0 +1,20 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+compile (
+	 v_flags2 => ["--lint-only"],
+	 fails=>$Self->{v3},
+	 expect=>
+q{%Error: t/t_select_bad_tri.v:\d+: Selection index is constantly unknown or tristated: lsb=7'bxxxxxxx width=\?32\?sh47
+%Error: Exiting due to.*},
+	 );
+
+ok(1);
+1;
+
diff --git a/test_regress/t/t_select_bad_tri.v b/test_regress/t/t_select_bad_tri.v
new file mode 100644
index 000000000..e7eed140e
--- /dev/null
+++ b/test_regress/t/t_select_bad_tri.v
@@ -0,0 +1,13 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2008 by Wilson Snyder.
+
+module t (/*AUTOARG*/);
+
+   reg [72:1] in;
+   initial begin
+      if (in[(   (1'h0 / 1'b0)   )+:71] != 71'h0) $stop;
+   end
+
+endmodule