diff --git a/docs/prefixes.md b/docs/prefixes.md
index 8ec8a48..18e9417 100644
--- a/docs/prefixes.md
+++ b/docs/prefixes.md
@@ -23,6 +23,7 @@ Below the list of possible parameters. **Remember to prepend them with a `--` in
 | -s  | A list of ASns to be monitored. See [monitorASns](#monitorASns) for more information | A comma separated list of integer | 2914,3333 | No |
 | -m  | Monitor all ASns which are origin of at least one of the monitored prefixes. This option is the same of `-s` except that the list of ASns is automatically generated by detecting the origin AS of all the monitored prefixes. See [monitorASns](#monitorASns) for more information | Nothing |  | No |
 | -x  | HTTP/HTTPS proxy server to use | A string | http://username:password@proxy.example.org:8080 | No |
+| -A  | Append the new configuration to the old one. E.g. you can use this option to add another AS. | Nothing |  | No |
 | -D  | Enable debug mode. All queries executed in background will be shown. | Nothing |  | No |
 | -H  | Use historical visibility data for generating prefix list (prefixes visible in the last week). Useful in case the prefix generation process returns an empty dataset. | Nothing |  | No |
 
diff --git a/index.js b/index.js
index 591212c..9387b3f 100644
--- a/index.js
+++ b/index.js
@@ -100,6 +100,10 @@ const params = yargs
             .nargs('g', 1)
             .describe('x', 'Define a user group for all the generated rules.')
 
+            .alias('A', 'append')
+            .nargs('A', 0)
+            .describe('A', 'Append the new configuration to the previous one.')
+
             .alias('D', 'debug')
             .nargs('D', 0)
             .describe('D', 'Provide verbose output for debugging')
@@ -157,7 +161,8 @@ switch(params._[0]) {
             httpProxy: params.x || null,
             debug,
             historical,
-            group: params.g
+            group: params.g,
+            append: !!params.A
         };
 
         generatePrefixes(inputParameters);
diff --git a/src/generatePrefixesList.js b/src/generatePrefixesList.js
index b827b0b..57ccf78 100644
--- a/src/generatePrefixesList.js
+++ b/src/generatePrefixesList.js
@@ -16,7 +16,8 @@ module.exports = function generatePrefixes(inputParameters) {
         httpProxy,
         debug,
         historical,
-        group
+        group,
+        append
     } = inputParameters;
 
     const generateList = {};
@@ -31,7 +32,7 @@ module.exports = function generatePrefixes(inputParameters) {
     if (historical) {
         console.log("WARNING: you are using historical visibility data for generating the prefix list.");
     }
-    
+
     if (!asnList && !prefixes) {
         throw new Error("You need to specify at least an AS number or a list of prefixes.");
     }
@@ -218,7 +219,7 @@ module.exports = function generatePrefixes(inputParameters) {
                 }
             })
             .catch(() => {
-                console.log("RIPEstat rpki-validation query failed: cannot retrieve information for " + prefix);
+                console.log("RPKI validation query failed: cannot retrieve information for " + prefix);
             });
     };
 
@@ -232,6 +233,34 @@ module.exports = function generatePrefixes(inputParameters) {
         }
     };
 
+    const getCurrentPrefixes = (outputFile, yamlContent) => {
+        const content = fs.readFileSync(outputFile, 'utf8');
+        const current = yaml.safeLoad(content) || {};
+
+        function isObject (item) {
+            return (item && typeof item === 'object' && !Array.isArray(item));
+        }
+        function mergeDeep(target, ...sources) {
+            if (!sources.length) return target;
+            const source = sources.shift();
+
+            if (isObject(target) && isObject(source)) {
+                for (const key in source) {
+                    if (isObject(source[key])) {
+                        if (!target[key]) Object.assign(target, { [key]: {} });
+                        mergeDeep(target[key], source[key]);
+                    } else {
+                        Object.assign(target, { [key]: source[key] });
+                    }
+                }
+            }
+
+            return mergeDeep(target, ...sources);
+        };
+
+        return mergeDeep(current, yamlContent);
+    };
+
     return getBaseRules()
         .then(items => [].concat.apply([], items))
         .then(prefixes => {
@@ -273,8 +302,13 @@ module.exports = function generatePrefixes(inputParameters) {
             // Otherwise nothing
         })
         .then(() => { // write everything into the file
-            const yamlContent = yaml.dump(generateList);
-            fs.writeFileSync(outputFile, yamlContent);
+
+            if (append) {
+                const finalList = getCurrentPrefixes(outputFile, generateList);
+                fs.writeFileSync(outputFile, yaml.dump(finalList));
+            } else {
+                fs.writeFileSync(outputFile, yaml.dump(generateList));
+            }
 
             if (someNotValidatedPrefixes) {
                 console.log("WARNING: the generated configuration is a snapshot of what is currently announced. Some of the prefixes don't have ROA objects associated or are RPKI invalid. Please, verify the config file by hand!");
diff --git a/src/inputs/input.js b/src/inputs/input.js
index 7bac3df..1edc3ea 100644
--- a/src/inputs/input.js
+++ b/src/inputs/input.js
@@ -206,7 +206,8 @@ export default class Input {
                                 httpProxy: null,
                                 debug: false,
                                 historical: false,
-                                group: null
+                                group: null,
+                                append: false
                             }
 
                             return generatePrefixes(inputParameters);