diff --git a/Makefile b/Makefile
index 80db525..448fa40 100644
--- a/Makefile
+++ b/Makefile
@@ -18,7 +18,9 @@ WARNFLAGS= -Wsystem-headers -Wall -W -Wno-unused-parameter \
 
 VER_FLAGS= -DMAJ_VER=$(MAJ_VER) -DMIN_VER=$(MIN_VER)
 
-CFLAGS=	$(WARNFLAGS) $(VER_FLAGS) -std=c99 -D_BSD_SOURCE
+INCDIR?=
+LIBDIR?=
+CFLAGS=	-I$(INCDIR) -L$(LIBDIR) $(WARNFLAGS) $(VER_FLAGS) -std=c99 -D_BSD_SOURCE
 CFLAGS_DEBUG= -O0 -g3
 CFLAGS_OPT=   -O4 -flto
 LDFLAGS=
diff --git a/README.md b/README.md
index b48964d..62dad3a 100644
--- a/README.md
+++ b/README.md
@@ -334,3 +334,7 @@ Just type
 
     make
 
+Or if your package manager installs software in a different place:
+
+    env INCDIR=/path/to/include LIBDIR=/path/to/lib make
+
diff --git a/calc.h b/calc.h
index 1bf0fcc..188043b 100644
--- a/calc.h
+++ b/calc.h
@@ -30,6 +30,7 @@
 #ifndef _CALC_H
 #define _CALC_H
 
+#include <stdio.h>
 #include "parse_ctx.h"
 
 #define MAX_HIST_LEN	1000
@@ -55,4 +56,6 @@ int yy_input_helper(char *buf, size_t max_size);
 int yyparse(struct parse_ctx *ctx);
 void mode_switch(char new_mode);
 void graceful_exit(void);
+int require_file(const char *, int);
+int require_fd(FILE *, const char *, int);
 #endif
diff --git a/calc.l b/calc.l
index 973aa69..09857b0 100644
--- a/calc.l
+++ b/calc.l
@@ -5,6 +5,8 @@
 %option bison-bridge
 %option bison-locations
 
+%option nounput
+
 %{
 # include <stdio.h>
 # include <assert.h>
@@ -20,6 +22,7 @@
 # include "parse_ctx.h"
 # include "calc.tab.h"
 
+#define YY_NO_INPUT
 #define YY_EXTRA_TYPE struct parse_ctx *
 #define YY_USER_ACTION yylloc->first_line = yylineno;
 
diff --git a/calc.y b/calc.y
index 908a1c7..72430c9 100644
--- a/calc.y
+++ b/calc.y
@@ -28,6 +28,7 @@
 #include "lex.yy.h"
 
 # define scanner ctx->scanner
+void yyerror(YYLTYPE *locp, struct parse_ctx *ctx, const char *s, ...);
 
 void
 yyerror(YYLTYPE *locp, struct parse_ctx *ctx, const char *s, ...)
diff --git a/main.c b/main.c
index 4940f70..9b83c83 100644
--- a/main.c
+++ b/main.c
@@ -204,7 +204,6 @@ sig_handler(int sig)
 	}
 }
 
-static
 int
 require_fd(FILE *fp, const char *fname, int silent)
 {
@@ -222,6 +221,7 @@ require_fd(FILE *fp, const char *fname, int silent)
 
 	return 0;
 }
+
 int
 require_file(const char *file, int silent)
 {
@@ -260,8 +260,6 @@ load_rc(void)
 {
 	struct dirent **namelist;
 	char p[4096];
-	FILE *fp;
-	DIR *dp;
 	int n;
 
 	/* Load rc file, if it exists */
@@ -282,7 +280,6 @@ int
 main(int argc, char *argv[])
 {
 	struct parse_ctx ctx;
-	char *progname = argv[0];
 	char *line;
 	int len;
 	int error;
diff --git a/num.c b/num.c
index fea6222..215eb09 100644
--- a/num.c
+++ b/num.c
@@ -84,8 +84,6 @@ static
 mpfr_prec_t
 num_prec(num_t a)
 {
-	mpfr_prec_t prec;
-
 	if (a != NULL && a->num_type == NUM_INT) {
 		/* XXX: completely arbitrary! */
 		return 2048;
diff --git a/parse_ctx.h b/parse_ctx.h
index 8cb2cfb..0696b42 100644
--- a/parse_ctx.h
+++ b/parse_ctx.h
@@ -2,7 +2,7 @@
 #define _PARSE_CTX_H
 
 struct parse_ctx {
-	char *filename;
+	const char *filename;
 	void *scanner;
 
 	int interactive;