diff --git a/src/V3Number.h b/src/V3Number.h
index 081644d45..2caba3e20 100644
--- a/src/V3Number.h
+++ b/src/V3Number.h
@@ -61,10 +61,8 @@ public:
 private:
     char bitIs	(int bit) const {
 	if (bit>=m_width) {
-	    bit = m_width-1;
 	    // We never sign extend
-	    return ( "00zx"[(((m_value[bit/32] & (1UL<<(bit&31)))?1:0)
-			     | ((m_valueX[bit/32] & (1UL<<(bit&31)))?2:0))] );
+	    return '0';
 	}
 	return ( "01zx"[(((m_value[bit/32] & (1UL<<(bit&31)))?1:0)
 			 | ((m_valueX[bit/32] & (1UL<<(bit&31)))?2:0))] ); }
diff --git a/test_regress/t/t_math_arith.v b/test_regress/t/t_math_arith.v
index 36f993e6e..f39fa0376 100644
--- a/test_regress/t/t_math_arith.v
+++ b/test_regress/t/t_math_arith.v
@@ -42,6 +42,10 @@ module t (/*AUTOARG*/
    wire       one = 1'b1;
    wire [5:0] rep6 = {6{one}};
 
+   // verilator lint_off WIDTH
+   localparam [3:0] bug764_p11 = 1'bx;
+   // verilator lint_on WIDTH
+
    always @ (posedge clk) begin
       if (!_ranit) begin
 	 _ranit <= 1;
@@ -119,6 +123,17 @@ module t (/*AUTOARG*/
 	 if ((~& 4'b1101) != 4'b0001) $stop;
 	 //verilator lint_on WIDTH
 
+	 // bug764
+	 //verilator lint_off WIDTH
+	 // X does not sign extend
+	 if (bug764_p11 !== 4'b000x) $stop;
+	 if (~& bug764_p11 !== 1'b1) $stop;
+	 //verilator lint_on WIDTH
+	 // However IEEE says for constants in 2012 5.7.1 that smaller-sizes do extend
+	 if (4'bx !== 4'bxxxx) $stop;
+	 if (4'bz !== 4'bzzzz) $stop;
+	 if (4'b1 !== 4'b0001) $stop;
+
 	 $write("*-* All Finished *-*\n");
 	 $finish;
       end