diff --git a/Makefile b/Makefile
index dab83bcbe..7883cf2b9 100644
--- a/Makefile
+++ b/Makefile
@@ -882,6 +882,7 @@ endif
 	+cd tests/memfile && bash run-test.sh
 	+cd tests/verilog && bash run-test.sh
 	+cd tests/xprop && bash run-test.sh $(SEEDOPT)
+	+cd tests/fmt && bash run-test.sh
 	@echo ""
 	@echo "  Passed \"make test\"."
 	@echo ""
diff --git a/tests/fmt/.gitignore b/tests/fmt/.gitignore
new file mode 100644
index 000000000..07043e547
--- /dev/null
+++ b/tests/fmt/.gitignore
@@ -0,0 +1,2 @@
+*.log
+iverilog-initial_display*
diff --git a/tests/fmt/initial_display.v b/tests/fmt/initial_display.v
new file mode 100644
index 000000000..26a39d0ec
--- /dev/null
+++ b/tests/fmt/initial_display.v
@@ -0,0 +1,245 @@
+module m;
+	initial $display("<<<BEGIN>>>");
+
+	initial $display("==> small unsigned %%d");
+	initial $display(":%d:",      16'haa);
+	initial $display(":%-d:",     16'haa);
+	initial $display(":%+d:",     16'haa);
+	initial $display(":%+-d:",    16'haa);
+	initial $display(":%0d:",     16'haa);
+	initial $display(":%-0d:",    16'haa);
+	initial $display(":%+0d:",    16'haa);
+	initial $display(":%+-0d:",   16'haa);
+	initial $display(":%20d:",    16'haa);
+	initial $display(":%-20d:",   16'haa);
+	initial $display(":%+20d:",   16'haa);
+	initial $display(":%+-20d:",  16'haa);
+	initial $display(":%020d:",   16'haa);
+	initial $display(":%-020d:",  16'haa);
+	initial $display(":%+020d:",  16'haa);
+	initial $display(":%+-020d:", 16'haa);
+
+	initial $display("==> big unsigned %%d");
+	initial $display(":%d:",      16'haaaa);
+	initial $display(":%-d:",     16'haaaa);
+	initial $display(":%+d:",     16'haaaa);
+	initial $display(":%+-d:",    16'haaaa);
+	initial $display(":%0d:",     16'haaaa);
+	initial $display(":%-0d:",    16'haaaa);
+	initial $display(":%+0d:",    16'haaaa);
+	initial $display(":%+-0d:",   16'haaaa);
+	initial $display(":%20d:",    16'haaaa);
+	initial $display(":%-20d:",   16'haaaa);
+	initial $display(":%+20d:",   16'haaaa);
+	initial $display(":%+-20d:",  16'haaaa);
+	initial $display(":%020d:",   16'haaaa);
+	initial $display(":%-020d:",  16'haaaa);
+	initial $display(":%+020d:",  16'haaaa);
+	initial $display(":%+-020d:", 16'haaaa);
+
+	initial $display("==> small signed %%d");
+	initial $display(":%d:",      16'shaa);
+	initial $display(":%-d:",     16'shaa);
+	initial $display(":%+d:",     16'shaa);
+	initial $display(":%+-d:",    16'shaa);
+	initial $display(":%0d:",     16'shaa);
+	initial $display(":%-0d:",    16'shaa);
+	initial $display(":%+0d:",    16'shaa);
+	initial $display(":%+-0d:",   16'shaa);
+	initial $display(":%20d:",    16'shaa);
+	initial $display(":%-20d:",   16'shaa);
+	initial $display(":%+20d:",   16'shaa);
+	initial $display(":%+-20d:",  16'shaa);
+	initial $display(":%020d:",   16'shaa);
+	initial $display(":%-020d:",  16'shaa);
+	initial $display(":%+020d:",  16'shaa);
+	initial $display(":%+-020d:", 16'shaa);
+
+	initial $display("==> big signed %%d");
+	initial $display(":%d:",      16'shaaaa);
+	initial $display(":%-d:",     16'shaaaa);
+	initial $display(":%+d:",     16'shaaaa);
+	initial $display(":%+-d:",    16'shaaaa);
+	initial $display(":%0d:",     16'shaaaa);
+	initial $display(":%-0d:",    16'shaaaa);
+	initial $display(":%+0d:",    16'shaaaa);
+	initial $display(":%+-0d:",   16'shaaaa);
+	initial $display(":%20d:",    16'shaaaa);
+	initial $display(":%-20d:",   16'shaaaa);
+	initial $display(":%+20d:",   16'shaaaa);
+	initial $display(":%+-20d:",  16'shaaaa);
+	initial $display(":%020d:",   16'shaaaa);
+	initial $display(":%-020d:",  16'shaaaa);
+	initial $display(":%+020d:",  16'shaaaa);
+	initial $display(":%+-020d:", 16'shaaaa);
+
+	initial $display("==> small unsigned %%h");
+	initial $display(":%h:",      16'haa);
+	initial $display(":%-h:",     16'haa);
+	initial $display(":%0h:",     16'haa);
+	initial $display(":%-0h:",    16'haa);
+	initial $display(":%20h:",    16'haa);
+	initial $display(":%-20h:",   16'haa);
+	initial $display(":%020h:",   16'haa);
+	initial $display(":%-020h:",  16'haa);
+
+	initial $display("==> big unsigned %%h");
+	initial $display(":%h:",      16'haaaa);
+	initial $display(":%-h:",     16'haaaa);
+	initial $display(":%0h:",     16'haaaa);
+	initial $display(":%-0h:",    16'haaaa);
+	initial $display(":%20h:",    16'haaaa);
+	initial $display(":%-20h:",   16'haaaa);
+	initial $display(":%020h:",   16'haaaa);
+	initial $display(":%-020h:",  16'haaaa);
+
+	initial $display("==> small signed %%h");
+	initial $display(":%h:",      16'shaa);
+	initial $display(":%-h:",     16'shaa);
+	initial $display(":%0h:",     16'shaa);
+	initial $display(":%-0h:",    16'shaa);
+	initial $display(":%20h:",    16'shaa);
+	initial $display(":%-20h:",   16'shaa);
+	initial $display(":%020h:",   16'shaa);
+	initial $display(":%-020h:",  16'shaa);
+
+	initial $display("==> big signed %%h");
+	initial $display(":%h:",      16'shaaaa);
+	initial $display(":%-h:",     16'shaaaa);
+	initial $display(":%0h:",     16'shaaaa);
+	initial $display(":%-0h:",    16'shaaaa);
+	initial $display(":%20h:",    16'shaaaa);
+	initial $display(":%-20h:",   16'shaaaa);
+	initial $display(":%020h:",   16'shaaaa);
+	initial $display(":%-020h:",  16'shaaaa);
+
+	initial $display("==> small unsigned %%o");
+	initial $display(":%o:",      16'haa);
+	initial $display(":%-o:",     16'haa);
+	initial $display(":%0o:",     16'haa);
+	initial $display(":%-0o:",    16'haa);
+	initial $display(":%20o:",    16'haa);
+	initial $display(":%-20o:",   16'haa);
+	initial $display(":%020o:",   16'haa);
+	initial $display(":%-020o:",  16'haa);
+
+	initial $display("==> big unsigned %%o");
+	initial $display(":%o:",      16'haaaa);
+	initial $display(":%-o:",     16'haaaa);
+	initial $display(":%0o:",     16'haaaa);
+	initial $display(":%-0o:",    16'haaaa);
+	initial $display(":%20o:",    16'haaaa);
+	initial $display(":%-20o:",   16'haaaa);
+	initial $display(":%020o:",   16'haaaa);
+	initial $display(":%-020o:",  16'haaaa);
+
+	initial $display("==> small signed %%o");
+	initial $display(":%o:",      16'shaa);
+	initial $display(":%-o:",     16'shaa);
+	initial $display(":%0o:",     16'shaa);
+	initial $display(":%-0o:",    16'shaa);
+	initial $display(":%20o:",    16'shaa);
+	initial $display(":%-20o:",   16'shaa);
+	initial $display(":%020o:",   16'shaa);
+	initial $display(":%-020o:",  16'shaa);
+
+	initial $display("==> big signed %%o");
+	initial $display(":%o:",      16'shaaaa);
+	initial $display(":%-o:",     16'shaaaa);
+	initial $display(":%0o:",     16'shaaaa);
+	initial $display(":%-0o:",    16'shaaaa);
+	initial $display(":%20o:",    16'shaaaa);
+	initial $display(":%-20o:",   16'shaaaa);
+	initial $display(":%020o:",   16'shaaaa);
+	initial $display(":%-020o:",  16'shaaaa);
+
+	initial $display("==> small unsigned %%b");
+	initial $display(":%b:",      16'haa);
+	initial $display(":%-b:",     16'haa);
+	initial $display(":%0b:",     16'haa);
+	initial $display(":%-0b:",    16'haa);
+	initial $display(":%20b:",    16'haa);
+	initial $display(":%-20b:",   16'haa);
+	initial $display(":%020b:",   16'haa);
+	initial $display(":%-020b:",  16'haa);
+
+	initial $display("==> big unsigned %%b");
+	initial $display(":%b:",      16'haaaa);
+	initial $display(":%-b:",     16'haaaa);
+	initial $display(":%0b:",     16'haaaa);
+	initial $display(":%-0b:",    16'haaaa);
+	initial $display(":%20b:",    16'haaaa);
+	initial $display(":%-20b:",   16'haaaa);
+	initial $display(":%020b:",   16'haaaa);
+	initial $display(":%-020b:",  16'haaaa);
+
+	initial $display("==> small signed %%b");
+	initial $display(":%b:",      16'shaa);
+	initial $display(":%-b:",     16'shaa);
+	initial $display(":%0b:",     16'shaa);
+	initial $display(":%-0b:",    16'shaa);
+	initial $display(":%20b:",    16'shaa);
+	initial $display(":%-20b:",   16'shaa);
+	initial $display(":%020b:",   16'shaa);
+	initial $display(":%-020b:",  16'shaa);
+
+	initial $display("==> big signed %%b");
+	initial $display(":%b:",      16'shaaaa);
+	initial $display(":%-b:",     16'shaaaa);
+	initial $display(":%0b:",     16'shaaaa);
+	initial $display(":%-0b:",    16'shaaaa);
+	initial $display(":%20b:",    16'shaaaa);
+	initial $display(":%-20b:",   16'shaaaa);
+	initial $display(":%020b:",   16'shaaaa);
+	initial $display(":%-020b:",  16'shaaaa);
+
+	initial $display("===> %%s");
+	initial $display(":%10s:", "foo");
+	initial $display(":%010s:", "foo");
+	initial $display(":%-10s:", "foo");
+	initial $display(":%-010s:", "foo");
+
+	initial $display("===> %%c");
+	initial $display(":%10c:", "foo");
+	initial $display(":%010c:", "foo");
+	initial $display(":%-10c:", "foo");
+	initial $display(":%-010c:", "foo");
+
+	initial $display("==> aliases");
+	initial $display(":%x:",      16'shaa);
+	initial $display(":%X:",      16'shaa);
+	initial $display(":%H:",      16'shaa);
+	initial $display(":%O:",      16'shaa);
+	initial $display(":%B:",      16'shaa);
+
+	initial $display("==> x/z");
+	initial $display(":%d:", 16'b1010101010101010);
+	initial $display(":%d:", 16'b101010101010101x);
+	initial $display(":%d:", 16'b101010101010101z);
+	initial $display(":%x:", 16'b1010101010101010);
+	initial $display(":%x:", 16'b101010101010101x);
+	initial $display(":%x:", 16'b101010101010101z);
+	initial $display(":%x:", 16'b101010101010xxxx);
+	initial $display(":%x:", 16'b101010101010zzzz);
+	initial $display(":%o:", 16'b1010101010101010);
+	initial $display(":%o:", 16'b101010101010101x);
+	initial $display(":%o:", 16'b101010101010101z);
+	initial $display(":%o:", 16'b1010101010101xxx);
+	initial $display(":%o:", 16'b1010101010101zzz);
+	initial $display(":%b:", 16'b1010101010101010);
+	initial $display(":%b:", 16'b101010101010101x);
+	initial $display(":%b:", 16'b101010101010101z);
+
+	initial $display("==> default base");
+	initial $displayh(16'haa);
+	initial $displayo(16'haa);
+	initial $displayb(16'haa);
+
+	initial $display("==> write/format");
+	initial $display("%d", 1, "%d", 1);
+	// this one hits a bug in iverilog:
+	// initial $display("%s", $sformatf("%d", 1, "%d", 1));
+
+	initial $display("<<<END>>>");
+
+endmodule
diff --git a/tests/fmt/run-test.sh b/tests/fmt/run-test.sh
new file mode 100644
index 000000000..c6bd111b2
--- /dev/null
+++ b/tests/fmt/run-test.sh
@@ -0,0 +1,6 @@
+#!/bin/bash -eu
+
+../../yosys initial_display.v | awk '/<<<BEGIN>>>/,/<<<END>>>/ {print $0}' >yosys-initial_display.log
+iverilog -o iverilog-initial_display initial_display.v
+./iverilog-initial_display >iverilog-initial_display.log
+diff yosys-initial_display.log iverilog-initial_display.log