diff --git a/tgt-vvp/draw_net_input.c b/tgt-vvp/draw_net_input.c
index dc2f14e54..6d527077d 100644
--- a/tgt-vvp/draw_net_input.c
+++ b/tgt-vvp/draw_net_input.c
@@ -388,10 +388,11 @@ static char* draw_net_input_drive(ivl_nexus_t nex, ivl_nexus_ptr_t nptr)
 		      number_is_immediate(d_fall, 64, 0) &&
 		      number_is_immediate(d_decay, 64, 0)) {
 
-			fprintf(vvp_out, "L_%p .delay (%lu,%lu,%lu) L_%p/d;\n",
-			                 cptr, get_number_immediate(d_rise),
-			                 get_number_immediate(d_rise),
-			                 get_number_immediate(d_rise), cptr);
+			fprintf(vvp_out, "L_%p .delay "
+				"(%" PRIu64 ",%" PRIu64 ",%" PRIu64 ") L_%p/d;\n",
+			                 cptr, get_number_immediate64(d_rise),
+			                 get_number_immediate64(d_rise),
+			                 get_number_immediate64(d_rise), cptr);
 
 		  } else {
 			ivl_signal_t sig;
diff --git a/tgt-vvp/eval_expr.c b/tgt-vvp/eval_expr.c
index 87c4201ca..12fb4abbd 100644
--- a/tgt-vvp/eval_expr.c
+++ b/tgt-vvp/eval_expr.c
@@ -131,6 +131,41 @@ long get_number_immediate(ivl_expr_t ex)
       return imm;
 }
 
+uint64_t get_number_immediate64(ivl_expr_t ex)
+{
+      uint64_t imm = 0;
+      unsigned idx;
+
+      switch (ivl_expr_type(ex)) {
+	  case IVL_EX_ULONG:
+	    imm = ivl_expr_uvalue(ex);
+	    break;
+
+	  case IVL_EX_NUMBER: {
+		const char*bits = ivl_expr_bits(ex);
+		unsigned nbits = ivl_expr_width(ex);
+		for (idx = 0 ; idx < nbits ; idx += 1) switch (bits[idx]){
+		    case '0':
+		      break;
+		    case '1':
+		      assert(idx < 64);
+		      imm |= UINT64_C(1) << idx;
+		      break;
+		    default:
+		      assert(0);
+		}
+		if (ivl_expr_signed(ex) && bits[nbits-1]=='1' && nbits < 64)
+		      imm |= -UINT64_C(1) << nbits;
+		break;
+	  }
+
+	  default:
+	    assert(0);
+      }
+
+      return imm;
+}
+
 static void eval_logic_into_integer(ivl_expr_t expr, unsigned ix)
 {
       switch (ivl_expr_type(expr)) {
diff --git a/tgt-vvp/vvp_priv.h b/tgt-vvp/vvp_priv.h
index b3ca6efd8..fda6bb5ad 100644
--- a/tgt-vvp/vvp_priv.h
+++ b/tgt-vvp/vvp_priv.h
@@ -271,6 +271,7 @@ extern unsigned allocate_vector_exp(ivl_expr_t exp, unsigned wid,
 extern int number_is_unknown(ivl_expr_t ex);
 extern int number_is_immediate(ivl_expr_t ex, unsigned lim_wid, int negative_is_ok);
 extern long get_number_immediate(ivl_expr_t ex);
+extern uint64_t get_number_immediate64(ivl_expr_t ex);
 
 /*
  * draw_eval_real evaluates real value expressions. The return code
diff --git a/vvp/README.txt b/vvp/README.txt
index 8c209b6a7..9c35a1c06 100644
--- a/vvp/README.txt
+++ b/vvp/README.txt
@@ -89,6 +89,10 @@ There are some special symbols that in certain contexts have special
 meanings. As inputs to functors, the symbols "C<0>", "C<1>", "C<x>"
 and "C<z>" represent a constant driver of the given value.
 
+NUMBERS:
+
+decimal number tokens are limited to 64bits, and are unsigned. Some
+contexts may constrain the number size further.
 
 SCOPE STATEMENTS:
 
@@ -375,10 +379,10 @@ times that are used for delay.
 	.delay ( <rise>, <fall>, <decay> ) <input> ;
 	.delay <input>, <rise>, <fall>, <decay> ;
 
-The first form above takes three constant numbers as the initial
-delay, and takes a single input. The second form takes 4 net inputs,
-with the first being the value to delay, and the remaining to be the
-delay values to use.
+The first form above takes three constant (64bit) numbers as the
+initial delay, and takes a single input. The second form takes 4 net
+inputs, with the first being the value to delay, and the remaining to
+be the delay values to use.
 
 MODULE PATH DELAY STATEMENTS:
 
diff --git a/vvp/lexor.lex b/vvp/lexor.lex
index 42f3c3a58..94d454115 100644
--- a/vvp/lexor.lex
+++ b/vvp/lexor.lex
@@ -32,6 +32,15 @@ static char* strdupnew(char const *str)
 {
       return str ? strcpy(new char [strlen(str)+1], str) : 0;
 }
+
+ inline uint64_t strtouint64(const char*str, char**endptr, int base)
+{
+      if (sizeof(unsigned long) >= sizeof(uint64_t))
+	    return strtoul(str, endptr, base);
+      else
+	    return strtoull(str, endptr, base);
+}
+
 %}
 
 %%
@@ -204,11 +213,11 @@ static char* strdupnew(char const *str)
       return T_INSTR; }
 
 [0-9][0-9]* {
-      yylval.numb = strtoul(yytext, 0, 0);
+      yylval.numb = strtouint64(yytext, 0, 0);
       return T_NUMBER; }
 
 "0x"[0-9a-fA-F]+ {
-      yylval.numb = strtoul(yytext, 0, 0);
+      yylval.numb = strtouint64(yytext, 0, 0);
       return T_NUMBER; }
 
   /* Handle some specialized constant/literals as symbols. */
diff --git a/vvp/parse.y b/vvp/parse.y
index d2a296b74..ae2454891 100644
--- a/vvp/parse.y
+++ b/vvp/parse.y
@@ -47,7 +47,7 @@ static struct __vpiModPath*modpath_dst = 0;
 %union {
       char*text;
       char **table;
-      unsigned long numb;
+      uint64_t numb;
       bool flag;
 
       comp_operands_t opa;