diff --git a/src/V3Undriven.cpp b/src/V3Undriven.cpp
index 36320fb0e..06636dfa8 100644
--- a/src/V3Undriven.cpp
+++ b/src/V3Undriven.cpp
@@ -75,7 +75,7 @@ public:
 
 private:
     // METHODS
-    inline bool bitNumOk(int bit) const { return (bit*FLAGS_PER_BIT < (int)m_flags.size()); }
+    inline bool bitNumOk(int bit) const { return bit>=0 && (bit*FLAGS_PER_BIT < (int)m_flags.size()); }
     inline bool usedFlag(int bit) const { return m_usedWhole || m_flags[bit*FLAGS_PER_BIT + FLAG_USED]; }
     inline bool drivenFlag(int bit) const { return m_drivenWhole || m_flags[bit*FLAGS_PER_BIT + FLAG_DRIVEN]; }
     enum BitNamesWhich { BN_UNUSED, BN_UNDRIVEN, BN_BOTH };
diff --git a/test_regress/t/t_select_runtime_range.v b/test_regress/t/t_select_runtime_range.v
index af2a5dc16..85e32018c 100644
--- a/test_regress/t/t_select_runtime_range.v
+++ b/test_regress/t/t_select_runtime_range.v
@@ -8,8 +8,27 @@ module t (clk);
 
    reg [43:0] mi;
    reg [5:0]  index;
+   integer    indexi;
    reg	      read;
 
+   initial begin
+      // Static
+      mi = 44'b01010101010101010101010101010101010101010101;
+      if (mi[0] !== 1'b1) $stop;
+      if (mi[1 -: 2] !== 2'b01) $stop;
+`ifdef VERILATOR
+      // verilator lint_off SELRANGE
+      if (mi[-1] !== 1'bx && mi[-1] !== 1'b0) $stop;
+      if (mi[0 -: 2] !== 2'b1x && 1'b0) $stop;
+      if (mi[-1 -: 2] !== 2'bxx && 1'b0) $stop;
+      // verilator lint_on SELRANGE
+`else
+      if (mi[-1] !== 1'bx) $stop;
+      if (mi[0 -: 2] !== 2'b1x) $stop;
+      if (mi[-1 -: 2] !== 2'bxx) $stop;
+`endif
+   end
+
    integer cyc; initial cyc=1;
    always @ (posedge clk) begin
       if (cyc!=0) begin
@@ -19,18 +38,33 @@ module t (clk);
 	 end
 	 if (cyc==2) begin
 	    index = 6'd43;
+	    indexi = 43;
 	 end
 	 if (cyc==3) begin
 	    read = mi[index];
 	    if (read!==1'b0) $stop;
+	    read = mi[indexi];
+	    if (read!==1'b0) $stop;
 	 end
 	 if (cyc==4) begin
 	    index = 6'd44;
+	    indexi = 44;
 	 end
 	 if (cyc==5) begin
 	    read = mi[index];
 	    $display("-Illegal read value: %x",read);
 	    //if (read!==1'b1 && read!==1'bx) $stop;
+	    read = mi[indexi];
+	    $display("-Illegal read value: %x",read);
+	    //if (read!==1'b1 && read!==1'bx) $stop;
+	 end
+	 if (cyc==6) begin
+	    indexi = -1;
+	 end
+	 if (cyc==7) begin
+	    read = mi[indexi];
+	    $display("-Illegal read value: %x",read);
+	    //if (read!==1'b1 && read!==1'bx) $stop;
 	 end
 	 if (cyc==10) begin
 	    $write("*-* All Finished *-*\n");