diff --git a/tools/qfcc/include/cpp.h b/tools/qfcc/include/cpp.h
index 46bb64e9e..8a1ba69e4 100644
--- a/tools/qfcc/include/cpp.h
+++ b/tools/qfcc/include/cpp.h
@@ -49,6 +49,7 @@ void intermediate_file (struct dstring_s *ifile, const char *filename,
 FILE *preprocess_file (const char *filename, const char *ext);
 extern const char *cpp_name;
 extern struct dstring_s *tempname;
+extern struct symtab_s *cpp_macros;
 
 void cpp_write_dependencies (const char *sourcefile);
 
diff --git a/tools/qfcc/include/rua-lang.h b/tools/qfcc/include/rua-lang.h
index d22186914..efcd13b1c 100644
--- a/tools/qfcc/include/rua-lang.h
+++ b/tools/qfcc/include/rua-lang.h
@@ -95,6 +95,7 @@ bool rua_defined (const char *sym, void *scanner);
 void rua_undefine (const char *sym, void *scanner);
 void rua_include_file (const char *name, void *scanner);
 void rua_embed_file (const char *name, void *scanner);
+int rua_parse_define (const char *def);
 
 #include "tools/qfcc/source/pre-parse.h"
 
diff --git a/tools/qfcc/source/cpp.c b/tools/qfcc/source/cpp.c
index 5f8c05867..c2b0d9ed5 100644
--- a/tools/qfcc/source/cpp.c
+++ b/tools/qfcc/source/cpp.c
@@ -62,7 +62,9 @@
 #include "tools/qfcc/include/diagnostic.h"
 #include "tools/qfcc/include/options.h"
 #include "tools/qfcc/include/qfcc.h"
+#include "tools/qfcc/include/rua-lang.h"
 #include "tools/qfcc/include/strpool.h"
+#include "tools/qfcc/include/symtab.h"
 
 typedef struct cpp_arg_s {
 	struct cpp_arg_s *next;
@@ -97,6 +99,7 @@ static bool cpp_dep_generate = false;
 static bool cpp_dep_phony = false;
 static bool cpp_dep_quote = false;
 
+symtab_t   *cpp_macros;
 const char *cpp_name = CPP_NAME;
 dstring_t  *tempname;
 
@@ -382,25 +385,38 @@ cpp_include (const char *opt, const char *arg)
 
 void cpp_define (const char *arg)
 {
-#if 0
 	if (!cpp_macros) {
-		cpp_macros = new_symtab (stab_global);
+		cpp_macros = new_symtab (0, stab_global);
 	}
-#endif
+	size_t len = strlen (arg);
+	if (len > 0x10000) {
+		error (0, "command line define too long: %zd", len);
+		return;
+	}
+	char argstr[len + 4];
+	strcpy (argstr, arg);
+	argstr[len] = '\n';
+	argstr[len + 1] = 0;
+	char *eq = strchr (argstr, '=');
+	if (eq) {
+		*eq = ' ';
+	} else {
+		strcpy (argstr + len, " 1\n");
+	}
+	rua_parse_define (argstr);
+
 	arg = va (0, "-D%s", arg);
 	CPP_ADD (def, arg);
 }
 
 void cpp_undefine (const char *arg)
 {
-#if 0
 	if (cpp_macros) {
 		auto sym = symtab_lookup (cpp_macros, arg);
 		if (sym) {
 			symtab_removesymbol (cpp_macros, sym);
 		}
 	}
-#endif
 	arg = va (0, "-D%s", arg);
 	CPP_ADD (undef, arg);
 }
diff --git a/tools/qfcc/source/qc-lex.l b/tools/qfcc/source/qc-lex.l
index f45540489..409663d3d 100644
--- a/tools/qfcc/source/qc-lex.l
+++ b/tools/qfcc/source/qc-lex.l
@@ -1110,7 +1110,7 @@ expand_macro (rua_extra_t *extra, rua_macro_t *macro)
 {
 	int         num_tokens = macro->num_tokens;
 	for (auto t = macro->tokens; t; t = t->next) {
-		if (t->token == -rua_id) {
+		if (t->token == -rua_id && macro->params) {
 			auto sym = symtab_lookup (macro->params, t->text);
 			if (sym) {
 				num_tokens += extra->arg_list.a[sym->s.offset]->num_tokens - 1;
@@ -1124,7 +1124,7 @@ expand_macro (rua_extra_t *extra, rua_macro_t *macro)
 	int         argid = 0;
 	for (auto t = macro->tokens; t; t = t->next) {
 		auto e = t;
-		if (t->token == -rua_id) {
+		if (t->token == -rua_id && macro->params) {
 			auto sym = symtab_lookup (macro->params, t->text);
 			if (sym) {
 				int  param = sym->s.offset;
@@ -1419,7 +1419,7 @@ qc_yyparse (FILE *in)
 		.arg_list = DARRAY_STATIC_INIT (8),
 		.include_stack = DARRAY_STATIC_INIT (8),
 		.dstr = dstring_new (),
-		.macro_tab = new_symtab (0, stab_global),
+		.macro_tab = cpp_macros ? cpp_macros : new_symtab (0, stab_global),
 	};
 
 	yylex_init_extra (&extra, &scanner);
@@ -1718,7 +1718,7 @@ dump_state_stack (void *scanner)
 			extra ? extra->recording ? "true" : "false" : "n/a",
 			extra ? extra->expand ? "true" : "false" : "n/a",
 			extra ? extra->params ? "true" : "false" : "n/a",
-			GETSTR(pr.source_file), pr.source_line);
+			pr.strings ? GETSTR(pr.source_file) : "", pr.source_line);
 }
 
 static void
@@ -1878,3 +1878,52 @@ rua_embed_file (const char *name, void *scanner)
 	internal_error (0, "not implemented");
 	(void)yy_top_state;
 }
+
+int
+rua_parse_define (const char *def)
+{
+	int         status;
+	yyscan_t    scanner;
+	rua_tok_t   tok = { .location = { 1, 1, 1, 1 }, };
+	rua_extra_t extra = {
+		.preprocessor = true,
+		.pre_state = pre_yypstate_new (),
+		.expr_stack = DARRAY_STATIC_INIT (32),
+		.macro_tab = cpp_macros,
+	};
+
+	yylex_init_extra (&extra, &scanner);
+	yy_scan_string (def, scanner);
+
+	yy_push_state (PREPROC, scanner);
+
+	int token = -1;
+	do {
+		if (token == -1) {
+			token = PRE_DEFINE;
+		} else {
+			token = yylex (&tok, &tok.location, scanner);
+			status = 0;
+		}
+		while (token) {
+			status = qc_process (&extra, token, &tok, scanner);
+			if (status != YYPUSH_MORE || !extra.expr_stack.size) {
+				break;
+			}
+			auto expr = DARRAY_REMOVE (&extra.expr_stack);
+			token = expr.token;
+			tok = (rua_tok_t) {
+				.location = expr.location,
+				.textlen = expr.textlen,
+				.text = expr.text,	// macro token strings use save_string
+				.token = token,
+			};
+		}
+	} while (status == YYPUSH_MORE);
+
+	yylex_destroy (scanner);
+	pre_yypstate_delete (extra.pre_state);
+	free (extra.expr_stack.a);
+	dstring_delete (extra.dstr);
+	return status;
+}