diff --git a/debian/changelog b/debian/changelog
index fa617c0..c54287c 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -13,6 +13,8 @@ dump1090-mutability (1.10.3010.14mu-11) UNRELEASED; urgency=medium
     discard bad position results.
   * Display message rate (30 sec average) on the webmap.
   * Restart lighttpd on package upgrade if we changed its config files.
+  * Require that the JSON refresh interval is at least 1, as it is used
+    to control the webmap refresh rate even if JSON files are not being written.
 
  -- Oliver Jowett <oliver@mutability.co.uk>  Sun, 11 Jan 2015 11:53:48 +0000
 
diff --git a/debian/dump1090-mutability.config b/debian/dump1090-mutability.config
index 517f63e..a55d2cc 100644
--- a/debian/dump1090-mutability.config
+++ b/debian/dump1090-mutability.config
@@ -108,6 +108,10 @@ is_unsigned_int_or_empty() {
   else return 1; fi
 }
 
+is_positive_int() {
+  if echo "$1" | grep -Eq '^(+?[1-9][0-9]*)$'; then return 0; else return 1; fi
+}
+
 is_signed_int() {
   if echo "$1" | grep -Eq '^(0|[+-]?[1-9][0-9]*)$'; then return 0; else return 1; fi
 }
@@ -201,13 +205,10 @@ db_go || true; db_get $NAME/auto-start; if [ "$RET" = "true" ]; then
  db_input_verify medium $NAME/net-bind-address is_ipaddrish_or_empty || true
 
  db_input_verify low $NAME/stats-interval is_unsigned_int || true
- db_input_verify low $NAME/json-interval is_unsigned_int || true
 
- db_go || true; db_get $NAME/json-interval; if [ -n "$RET" ] && [ "$RET" -gt 0 ]; then
-  # only if json-interval was given and non-zero
-  db_input low $NAME/json-dir || true
-  db_input low $NAME/json-location-accuracy || true
- fi
+ db_input_verify low $NAME/json-interval is_positive_int || true
+ db_input low $NAME/json-location-accuracy || true
+ db_input low $NAME/json-dir || true
 
  db_input low $NAME/log-decoded-messages || true
  db_input low $NAME/extra-args || true
diff --git a/debian/dump1090-mutability.templates b/debian/dump1090-mutability.templates
index 04c12ea..e6c450b 100644
--- a/debian/dump1090-mutability.templates
+++ b/debian/dump1090-mutability.templates
@@ -235,6 +235,8 @@ Description: Directory to write JSON aircraft state to:
  As this can be written frequently, you should select a location
  that is not on a sdcard. The default path under /run is on tmpfs
  and will not write to the sdcard.
+ .
+ A blank path disables writing JSON state.
 Type: string
 Default: /run/dump1090-mutability
 
@@ -246,8 +248,6 @@ Description: Interval between writing JSON aircraft state, in seconds:
  .
  Here you can control how often the JSON state is updated, which determines
  how frequently the virtual radar view updates.
- .
- A value of 0 will disable writing JSON state entirely.
 Type: string
 Default: 1
 
@@ -293,6 +293,10 @@ Template: dump1090-mutability/invalid-is_unsigned_int_or_empty
 Description: Value must be an unsigned integer, or blank.
 Type: error
 
+Template: dump1090-mutability/invalid-is_positive_int
+Description: Value must be a positive integer.
+Type: error
+
 Template: dump1090-mutability/invalid-is_signed_int
 Description: Value must be an integer.
 Type: error
diff --git a/dump1090.c b/dump1090.c
index 1d22a5d..b034102 100644
--- a/dump1090.c
+++ b/dump1090.c
@@ -667,7 +667,7 @@ void backgroundTasks(void) {
         }
     }
 
-    if (Modes.json_aircraft_path && Modes.json_interval > 0) {
+    if (Modes.json_aircraft_path) {
         time_t now = time(NULL);
         if (now >= next_json) {
             writeJsonToFile(Modes.json_aircraft_path, generateAircraftJson);
@@ -879,6 +879,8 @@ int main(int argc, char **argv) {
             strcat(Modes.json_metadata_path, "/receiver.json");
         } else if (!strcmp(argv[j], "--write-json-every") && more) {
             Modes.json_interval = atoi(argv[++j]);
+            if (Modes.json_interval < 1)
+                Modes.json_interval = 1;
         } else if (!strcmp(argv[j], "--json-location-accuracy") && more) {
             Modes.json_location_accuracy = atoi(argv[++j]);
 #endif
@@ -932,7 +934,7 @@ int main(int argc, char **argv) {
     }
     if (Modes.net) modesInitNet();
 
-    if (Modes.json_metadata_path && Modes.json_interval > 0) {
+    if (Modes.json_metadata_path) {
         writeJsonToFile(Modes.json_metadata_path, generateReceiverJson); // once only on startup
     }