diff --git a/vpi/sdf_lexor.lex b/vpi/sdf_lexor.lex
index c4b03d3fe..d0e231592 100644
--- a/vpi/sdf_lexor.lex
+++ b/vpi/sdf_lexor.lex
@@ -126,6 +126,7 @@ static struct {
       { "IOPATH",     K_IOPATH },
       { "PROCESS",    K_PROCESS },
       { "PROGRAM",    K_PROGRAM },
+      { "RECREM",     K_RECREM },
       { "RECOVERY",   K_RECOVERY },
       { "REMOVAL",    K_REMOVAL },
       { "SDFVERSION", K_SDFVERSION },
diff --git a/vpi/sdf_parse.y b/vpi/sdf_parse.y
index e929252bb..3b10fea5c 100644
--- a/vpi/sdf_parse.y
+++ b/vpi/sdf_parse.y
@@ -45,9 +45,9 @@ char sdf_use_hchar = '.';
 
 %token K_ABSOLUTE K_CELL K_CELLTYPE K_DATE K_DELAYFILE K_DELAY K_DESIGN
 %token K_DIVIDER K_HOLD K_INCREMENT K_INSTANCE K_INTERCONNECT K_IOPATH
-%token K_NEGEDGE K_POSEDGE K_PROCESS K_PROGRAM K_RECOVERY K_REMOVAL
-%token K_SDFVERSION K_SETUP K_SETUPHOLD K_TEMPERATURE K_TIMESCALE
-%token K_TIMINGCHECK K_VENDOR K_VERSION K_VOLTAGE K_WIDTH
+%token K_NEGEDGE K_POSEDGE K_PROCESS K_PROGRAM K_RECREM K_RECOVERY
+%token K_REMOVAL K_SDFVERSION K_SETUP K_SETUPHOLD K_TEMPERATURE
+%token K_TIMESCALE K_TIMINGCHECK K_VENDOR K_VERSION K_VOLTAGE K_WIDTH
 %token K_01 K_10 K_0Z K_Z1 K_1Z K_Z0
 
 %token HCHAR
@@ -60,8 +60,8 @@ char sdf_use_hchar = '.';
 %type <string_val> hierarchical_identifier
 %type <string_val> port port_instance port_interconnect
 
-%type <real_val> rtriple signed_real_number
-%type <delay> delval rvalue
+%type <real_val> signed_real_number
+%type <delay> delval rvalue rtriple signed_real_number_opt
 
 %type <int_val> edge_identifier
 %type <port_with_edge> port_edge port_spec
@@ -284,6 +284,7 @@ tchk_def
   | '(' K_SETUPHOLD port_tchk port_tchk rvalue rvalue ')'
   | '(' K_RECOVERY port_tchk port_tchk rvalue ')'
   | '(' K_REMOVAL port_tchk port_tchk rvalue ')'
+  | '(' K_RECREM port_tchk port_tchk rvalue rvalue ')'
   | '(' K_WIDTH port_tchk rvalue ')'
   ;
 
@@ -369,8 +370,7 @@ rvalue
       { $$.defined = 1;
         $$.value = $2; }
   | '(' rtriple ')'
-      { $$.defined = 1;
-        $$.value = $2; }
+      { $$ = $2; }
   | '(' ')'
       { $$.defined = 0;
         $$.value = 0.0; }
@@ -390,7 +390,7 @@ hierarchical_identifier
   ;
 
 rtriple
-  : signed_real_number ':' signed_real_number ':' signed_real_number
+  : signed_real_number_opt ':' signed_real_number_opt ':' signed_real_number_opt
       { switch(sdf_min_typ_max) {
 	    case _vpiDelaySelMinimum:
 	       $$ = $1;
@@ -402,9 +402,24 @@ rtriple
 	       $$ = $5;
 	       break;
 	}
+	  /* At least one of the values must be defined. */
+	if (! ($1.defined || $3.defined || $5.defined)) {
+	      vpi_printf("%s:%d: SDF ERROR: rtriple must have at least one "
+	                 "defined value.\n", sdf_parse_path, @1.first_line);
+	}
       }
   ;
 
+signed_real_number_opt
+  : /* When missing. */
+      { $$.value = 0.0;
+	$$.defined = 0;
+      }
+  | signed_real_number
+      { $$.value = $1;
+	$$.defined = 1;
+      }
+
 signed_real_number
   :     REAL_NUMBER { $$ = $1; }
   | '+' REAL_NUMBER { $$ = $2; }