Index: class.c
==================================================================
--- class.c
+++ class.c
@@ -612,12 +612,18 @@
   if(!inpstack) fatal("Allocation failed\n");
   inpstack->classfp=classfp;
   inpstack->linenum=linenum;
   inpstack->next=nxt;
   linenum=1;
-  //TODO: Use the correct directory to load the include file
-  classfp=fopen(name,"r");
+  if(*name=='.' || *name=='_' || *name=='-' || !*name || name[strspn(name,"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_-")])
+   ParseError("Improper name of include file \"%s\"\n",name);
+  if(main_options['z']) {
+    if(strlen(name)<9 || memcmp(name-strlen(name),".include",8)) ParseError("Include file name doesn't end with .include\n");
+    classfp=composite_slice(name,0)?:fopen(name,"r");
+  } else {
+    classfp=fopen(name,"r");
+  }
   if(!classfp) ParseError("Cannot open include file \"%s\": %m\n",name);
 }
 
 static void begin_macro(TokenList*mac) {
   MacroStack*ms=malloc(sizeof(MacroStack));

Index: class.doc
==================================================================
--- class.doc
+++ class.doc
@@ -188,11 +188,16 @@
   not be another macro). The token is expanded, and must be a single token
   once it is expanded; that is what it will be replaced with.
 
 {include <string>}
   Include text from another file into this one. You cannot use {include}
-  inside of another macro or in a macro argument.
+  inside of another macro or in a macro argument. The file must be in the
+  current directory, and its name must contain only letters, digits, dot,
+  underscore, and minus signs, and must start with a letter or digit. If
+  it is a composite puzzle set, then the name must end with ".include",
+  and is looked for first inside of the composite puzzle set; if it is not
+  found there then it is looked for in the current directory.
 
 {make <mode> <arg>}
   Make a synthetic token; see the below section about synthetic tokens for
   details. The second argument can be a number, or a direction or key name
   which is treated as a number, or a string. In most cases, a number will