diff --git a/calc.c b/calc.c
index 742c20c..21c9434 100644
--- a/calc.c
+++ b/calc.c
@@ -168,9 +168,10 @@ main(int argc, char **argv)
 					/*
 					 * error if libcustcalc was compiled with CUSTOM undefined
 					 */
-					if (custom_compiled() == 0) {
-					    fprintf(stderr, "%s: calc was built with custom functions enabled, "
-							    "however custom_compiled() retuned 0", program);
+					if (custom_compiled() != TRUE) {
+					    math_error("%s: calc was built with custom functions enabled, "
+						       "custom_compiled() returned: %d != %d",
+						       program, custom_compiled(), TRUE);
 					    exit(1);
 					}
 
@@ -184,9 +185,10 @@ main(int argc, char **argv)
 					/*
 					 * error if libcustcalc was compiled with CUSTOM defined
 					 */
-					if (custom_compiled() == 1) {
-					    fprintf(stderr, "%s: calc was built with custom functions disabled, "
-							    "however custom_compiled() retuned 1", program);
+					if (custom_compiled() != FALSE) {
+					    math_error("%s: calc was built with custom functions disabled, "
+						       "custom_compiled() returned: %d != %d",
+						       program, custom_compiled(), FALSE);
 					}
 
 					/*
diff --git a/custom.c b/custom.c
index f9feedf..e26159e 100644
--- a/custom.c
+++ b/custom.c
@@ -71,8 +71,10 @@ custom(char *name, int count, VALUE **vals)
 	/*
 	 * error if libcustcalc was compiled with CUSTOM undefined
 	 */
-	if (custom_compiled() == 0) {
-	    math_error("libcustcalc was compiled CUSTOM undefined");
+	if (custom_compiled() != TRUE) {
+	    math_error("libcustcalc was compiled with CUSTOM undefined "
+		       "custom_compiled() returned: %d != %d",
+		       custom_compiled(), TRUE);
 	    not_reached();
 	}
 
@@ -111,8 +113,10 @@ custom(char *name, int count, VALUE **vals)
 	/*
 	 * error if libcustcalc was compiled with CUSTOM defined
 	 */
-	if (custom_compiled() == 1) {
-	    math_error("libcustcalc was compiled with CUSTOM defined");
+	if (custom_compiled() != FALSE) {
+	    math_error("libcustcalc was compiled with CUSTOM defined "
+		       "custom_compiled() returned: %d != %d",
+		       custom_compiled(), FALSE);
 	    not_reached();
 	}
 
diff --git a/custom.h b/custom.h
index d5aa9ad..65d358e 100644
--- a/custom.h
+++ b/custom.h
@@ -73,7 +73,7 @@ struct custom {
  *
  * These are the required interfaces.  The dummy.c stubs these interfaces too.
  */
-E_FUNC int custom_compiled(void);	/* return 1 ==> libcustcalc compiled w/CUSTOM defined, else return 0 */
+E_FUNC BOOL custom_compiled(void);	/* return TRUE if libcustcalc compiled CUSTOM defined, FALSE otherwise */
 E_FUNC VALUE custom(char*, int, VALUE**);	/* master custom interface */
 EXTERN BOOL allow_custom;		/* TRUE => custom builtins allowed */
 E_FUNC void showcustom(void);		/* print custom functions */
diff --git a/custom/custtbl.c b/custom/custtbl.c
index e2c16ba..2219982 100644
--- a/custom/custtbl.c
+++ b/custom/custtbl.c
@@ -39,16 +39,16 @@
  * custom_compiled - determine if custom functions are compiled into libcustcalc
  *
  * returns:
-s*	1 ==> libcustcalc was compiled with CUSTOM defined
- *	0 ==> libcustcalc was compiled with CUSTOM undefined
+s*	TRUE  ==> libcustcalc was compiled with CUSTOM defined
+ *	FALSE ==> libcustcalc was compiled with CUSTOM undefined
  */
-E_FUNC int
+E_FUNC BOOL
 custom_compiled(void)
 {
 #if defined(CUSTOM)
-	return 1;
+	return TRUE;
 #else /* CUSTOM */
-	return 0;
+	return FALSE;
 #endif /* CUSTOM */
 }