diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 19e62668b..ee1be3781 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -48,22 +48,27 @@ Fmt AstNode::processFormat(int stage, bool sformat_like, int default_base, size_
 	for (size_t index = first_arg_at; index < children.size(); index++) {
 		AstNode *node_arg = children[index];
 		while (node_arg->simplify(true, false, stage, -1, false, false)) { }
-		if (node_arg->type != AST_CONSTANT)
-			input_error("Failed to evaluate system task `%s' with non-constant argument at position %zu.\n", str.c_str(), index + 1);
 
 		VerilogFmtArg arg = {};
 		arg.filename = filename;
 		arg.first_line = location.first_line;
-		if (node_arg->is_string) {
+		if (node_arg->type == AST_CONSTANT && node_arg->is_string) {
 			arg.type = VerilogFmtArg::STRING;
 			arg.str = node_arg->bitsAsConst().decode_string();
 			// and in case this will be used as an argument...
 			arg.sig = node_arg->bitsAsConst();
 			arg.signed_ = false;
-		} else {
+		} else if (node_arg->type == AST_IDENTIFIER && node_arg->str == "$time") {
+			arg.type = VerilogFmtArg::TIME;
+		} else if (node_arg->type == AST_IDENTIFIER && node_arg->str == "$realtime") {
+			arg.type = VerilogFmtArg::TIME;
+			arg.realtime = true;
+		} else if (node_arg->type == AST_CONSTANT) {
 			arg.type = VerilogFmtArg::INTEGER;
 			arg.sig = node_arg->bitsAsConst();
 			arg.signed_ = node_arg->is_signed;
+		} else {
+			log_file_error(filename, location.first_line, "Failed to evaluate system task `%s' with non-constant argument at position %zu.\n", str.c_str(), index + 1);
 		}
 		args.push_back(arg);
 	}
diff --git a/kernel/fmt.cc b/kernel/fmt.cc
index 9d9e95ac3..0fac64175 100644
--- a/kernel/fmt.cc
+++ b/kernel/fmt.cc
@@ -606,6 +606,7 @@ std::string Fmt::render() const
 				break;
 
 			case FmtPart::INTEGER:
+			case FmtPart::TIME:
 			case FmtPart::CHARACTER: {
 				std::string buf;
 				if (part.type == FmtPart::INTEGER) {
@@ -689,6 +690,9 @@ std::string Fmt::render() const
 					} else log_abort();
 				} else if (part.type == FmtPart::CHARACTER) {
 					buf = part.sig.as_const().decode_string();
+				} else if (part.type == FmtPart::TIME) {
+					// We only render() during initial, so time is always zero.
+					buf = "0";
 				}
 
 				log_assert(part.width == 0 || part.padding != '\0');
@@ -705,12 +709,6 @@ std::string Fmt::render() const
 					str += std::string(part.width - buf.size(), part.padding);
 				break;
 			}
-
-			case FmtPart::TIME: {
-				// We only render() during initial, so time is always zero.
-				str += "0";
-				break;
-			}
 		}
 	}
 
diff --git a/tests/fmt/initial_display.v b/tests/fmt/initial_display.v
index 26a39d0ec..d3ef9ed76 100644
--- a/tests/fmt/initial_display.v
+++ b/tests/fmt/initial_display.v
@@ -193,6 +193,16 @@ module m;
 	initial $display(":%020b:",   16'shaaaa);
 	initial $display(":%-020b:",  16'shaaaa);
 
+	initial $display("==> time %%t");
+	initial $display(":%t:",      $time);
+	initial $display(":%-t:",     $time);
+	initial $display(":%0t:",     $time);
+	initial $display(":%-0t:",    $time);
+	initial $display(":%10t:",    $time);
+	initial $display(":%-10t:",   $time);
+	initial $display(":%015t:",   $time);
+	initial $display(":%-015t:",  $time);
+
 	initial $display("===> %%s");
 	initial $display(":%10s:", "foo");
 	initial $display(":%010s:", "foo");