diff --git a/driver/iverilog.man b/driver/iverilog.man
index 672f54252..d9bffeaca 100644
--- a/driver/iverilog.man
+++ b/driver/iverilog.man
@@ -338,6 +338,12 @@ and directory strings.
 
 Variable values come from the operating system environment, and not
 from preprocessor defines elsewhere in the file or the command line.
+ 
+.SH PREDEFINED MACROS
+
+The following macro is predefined by the compiler:
+.TP 8
+.B __ICARUS__ = 1\fP
 
 .SH EXAMPLES
 These examples assume that you have a Verilog source file called hello.v in