diff --git a/iverilog-vpi.man b/iverilog-vpi.man
index f49af2d7f..fb559691f 100644
--- a/iverilog-vpi.man
+++ b/iverilog-vpi.man
@@ -27,6 +27,15 @@ first source file is named \fIfoo.c\fP, the output becomes
 Include the named library in the link of the VPI module. This allows
 VPI modules to further reference external libraries.
 
+.TP 8
+.B -I\fIdirectory\fP
+Add \fIdirectory\fP to the list of directories that will be search for
+header files.
+
+.TP 8
+.B -D\fIdefine\fP
+Define a macro named \fIdefine\fP.
+
 .TP 8
 .B --name=\fIname\fP
 Normally, the output VPI module will be named after the first source
@@ -39,6 +48,10 @@ This flag causes the program to print the install directory for VPI
 modules, then exit. It is a convenience for makefiles or automated
 plug-in installers.
 
+.TP 8
+.B --cflags, --ldflags and -ldlibs
+These flags provide compile time information.
+
 .SH "PC-ONLY OPTIONS"
 
 The PC port of \fIiverilog-vpi\fP includes two special flags needed to
diff --git a/iverilog-vpi.sh b/iverilog-vpi.sh
index c82689a4f..fbccedb04 100644
--- a/iverilog-vpi.sh
+++ b/iverilog-vpi.sh
@@ -46,6 +46,7 @@ OBJ=
 LIB=
 OUT=
 INCOPT=
+DEFS=
 
 # --
 # parse the command line switches. This collects the source files
@@ -90,7 +91,9 @@ do
 	 ;;
 
     -I*) INCOPT="$INCOPT $parm"
-	 echo "$parm"
+	 ;;
+
+    -D*) DEFS="$DEFS $parm"
 	 ;;
 
     -m32) LDFLAGS="-m32 $LDFLAGS32"
@@ -138,7 +141,7 @@ do
     obj=$base".o"
 
     echo "Compiling $src..."
-    $CC -c -o $obj $CFLAGS $INCOPT $src || compile_errors=`expr $compile_errors + 1`
+    $CC -c -o $obj $DEFS $CFLAGS $INCOPT $src || compile_errors=`expr $compile_errors + 1`
     OBJ="$OBJ $obj"
 done
 
@@ -148,7 +151,7 @@ do
     obj=$base".o"
 
     echo "Compiling $src..."
-    $CXX -c -o $obj $CFLAGS $INCOPT $src || compile_errors=`expr $compile_errors + 1`
+    $CXX -c -o $obj $DEFS $CFLAGS $INCOPT $src || compile_errors=`expr $compile_errors + 1`
     OBJ="$OBJ $obj"
 done