diff --git a/usr.bin/calendar/calendar.1 b/usr.bin/calendar/calendar.1
index cf2db36ca4de..240c74d571fe 100644
--- a/usr.bin/calendar/calendar.1
+++ b/usr.bin/calendar/calendar.1
@@ -28,7 +28,7 @@
 .\"     @(#)calendar.1  8.1 (Berkeley) 6/29/93
 .\" $FreeBSD$
 .\"
-.Dd October 25, 2020
+.Dd October 28, 2020
 .Dt CALENDAR 1
 .Os
 .Sh NAME
@@ -198,7 +198,13 @@ file is preprocessed by a limited subset of
 .Xr cpp 1
 internally, allowing the inclusion of shared files such as
 lists of company holidays or meetings.
-This limited subset consists of \fB#include #ifndef #endif\fR and \fB#define\fR.
+This limited subset consists of \fB#include #ifdef #ifndef #else
+#endif\fR and \fB#define\fR. Conditions can be nested, but not check
+for matching begin and end directives is performed.
+Included files are parsed in their own scope.
+They have no read or write access to condition variables defined in
+an outer scope and open conditional blocks are implicitly closed.
+.Pp
 If the shared file is not referenced by a full pathname,
 .Nm
 searches in the current (or home) directory first, and then in the
@@ -346,9 +352,12 @@ double-check the start and end time of solar and lunar events.
 .Sh BUGS
 The
 .Nm
-internal cpp does not support nested conditions and will continue
-parsing of the input file on the next #endif even in nested contexts.
-It does only recognise #include, #define, #ifdef and #ifndef.
+does only recognise the cpp directives #include, #define, #ifdef,
+#ifndef and #else.
+It supports nested conditions, but does not perform any validation
+on the correct use and nesting of conditions.
+#endif without prior #ifdef or #define is ignored and #else outside
+a conditional section skips input lines up to the next #endif.
 .Pp
 There is no possibility to properly specify the local position
 needed for solar and lunar calculations.
diff --git a/usr.bin/calendar/io.c b/usr.bin/calendar/io.c
index 25cf9b5d451a..6efbc5ca72a5 100644
--- a/usr.bin/calendar/io.c
+++ b/usr.bin/calendar/io.c
@@ -140,16 +140,64 @@ cal_fopen(const char *file)
 }
 
 static int
-token(char *line, FILE *out, bool *skip)
+token(char *line, FILE *out, int *skip)
 {
 	char *walk, c, a;
 
 	if (strncmp(line, "endif", 5) == 0) {
-		*skip = false;
+		if (*skip > 0)
+			--*skip;
 		return (T_OK);
 	}
 
-	if (*skip)
+	if (strncmp(line, "ifdef", 5) == 0) {
+		walk = line + 5;
+		trimlr(&walk);
+
+		if (*walk == '\0') {
+			warnx("Expecting arguments after #ifdef");
+			return (T_ERR);
+		}
+
+		if (*skip != 0 || definitions == NULL || sl_find(definitions, walk) == NULL)
+			++*skip;
+
+		return (T_OK);
+	}
+
+	if (strncmp(line, "ifndef", 6) == 0) {
+		walk = line + 6;
+		trimlr(&walk);
+
+		if (*walk == '\0') {
+			warnx("Expecting arguments after #ifndef");
+			return (T_ERR);
+		}
+
+		if (*skip != 0 || (definitions != NULL && sl_find(definitions, walk) != NULL))
+			++*skip;
+
+		return (T_OK);
+	}
+
+	if (strncmp(line, "else", 4) == 0) {
+		walk = line + 4;
+		trimlr(&walk);
+
+		if (*walk != '\0') {
+			warnx("Expecting no arguments after #else");
+			return (T_ERR);
+		}
+
+		if (*skip == 0)
+			*skip = 1;
+		else if (*skip == 1)
+			*skip = 0;
+
+		return (T_OK);
+	}
+
+	if (*skip != 0)
 		return (T_OK);
 
 	if (strncmp(line, "include", 7) == 0) {
@@ -212,36 +260,6 @@ token(char *line, FILE *out, bool *skip)
 		return (T_OK);
 	}
 
-	if (strncmp(line, "ifdef", 5) == 0) {
-		walk = line + 5;
-		trimlr(&walk);
-
-		if (*walk == '\0') {
-			warnx("Expecting arguments after #ifdef");
-			return (T_ERR);
-		}
-
-		if (definitions == NULL || sl_find(definitions, walk) == NULL)
-			*skip = true;
-
-		return (T_OK);
-	}
-
-	if (strncmp(line, "ifndef", 6) == 0) {
-		walk = line + 6;
-		trimlr(&walk);
-
-		if (*walk == '\0') {
-			warnx("Expecting arguments after #ifndef");
-			return (T_ERR);
-		}
-
-		if (definitions != NULL && sl_find(definitions, walk) != NULL)
-			*skip = true;
-
-		return (T_OK);
-	}
-
 	return (T_PROCESS);
 
 }
@@ -269,7 +287,7 @@ cal_parse(FILE *in, FILE *out)
 	int month[MAXCOUNT];
 	int day[MAXCOUNT];
 	int year[MAXCOUNT];
-	bool skip = false;
+	int skip = 0;
 	char dbuf[80];
 	char *pp, p;
 	struct tm tm;
@@ -299,7 +317,7 @@ cal_parse(FILE *in, FILE *out)
 			}
 		}
 
-		if (skip)
+		if (skip != 0)
 			continue;
 
 		buf = line;