diff --git a/opensprinkler_server.cpp b/opensprinkler_server.cpp
index 44e716d3..e21976d0 100644
--- a/opensprinkler_server.cpp
+++ b/opensprinkler_server.cpp
@@ -910,6 +910,15 @@ void server_change_program(OTF_PARAMS_DEF) {
 	*(char*)(&prog) = parse_listdata(&pv);
 	prog.days[0]= parse_listdata(&pv);
 	prog.days[1]= parse_listdata(&pv);
+	
+	if (prog.type == PROGRAM_TYPE_INTERVAL) {
+		if (prog.days[1] == 0) handle_return(HTML_DATA_OUTOFBOUND)
+		else if (prog.days[1] >= 1) {
+			// process interval day remainder (relative-> absolute)
+			pd.drem_to_absolute(prog.days);
+		}
+	}
+
 	// parse start times
 	pv++; // this should be a '['
 	for (i=0;i<MAX_NUM_STARTTIMES;i++) {
@@ -930,11 +939,6 @@ void server_change_program(OTF_PARAMS_DEF) {
 		prog.durations[i] = 0;		 // clear unused field
 	}
 
-	// process interval day remainder (relative-> absolute)
-	if (prog.type == PROGRAM_TYPE_INTERVAL && prog.days[1] >= 1) {
-		pd.drem_to_absolute(prog.days);
-	}
-
 	if (pid==-1) {
 		if(!pd.add(&prog)) handle_return(HTML_DATA_OUTOFBOUND);
 	} else {
diff --git a/program.h b/program.h
index b3d6d8db..f2dea6aa 100644
--- a/program.h
+++ b/program.h
@@ -81,7 +81,7 @@ class ProgramStruct {
 	// weekly:   days[0][0..6] correspond to Monday till Sunday
 	// bi-weekly:days[0][0..6] and [1][0..6] store two weeks
 	// monthly:  days[0][0..5] stores the day of the month (32 means last day of month)
-	// interval: days[0] stores the interval (0 to 255), days[1] stores the starting day remainder (0 to 254)
+	// interval: days[1] stores the interval (0 to 255), days[0] stores the starting day remainder (0 to 254)
 	unsigned char days[2];
 
 	// When the program is a fixed start time type: