diff --git a/webinstall/build.yaml b/webinstall/build.yaml
index 566e314..99a0881 100644
--- a/webinstall/build.yaml
+++ b/webinstall/build.yaml
@@ -146,9 +146,11 @@ types:
                 - <<: *gpiopin
                   key: RX
                   target: "define:GWSERIAL_RX"
+                  mandatory: true
                 - <<: *gpiopin
                   key: TX
                   target: "define:GWSERIAL_TX"
+                  mandatory: true
             - key: bi
               value: 2
               label: "BiDir" 
@@ -157,9 +159,11 @@ types:
                 - <<: *gpiopin
                   key: RX
                   target: "define:GWSERIAL_RX"
+                  mandatory: true
                 - <<: *gpiopin
                   key: TX
                   target: "define:GWSERIAL_TX"
+                  mandatory: true
             - key: rx
               value: 3
               label: "RX"    
@@ -168,6 +172,7 @@ types:
                 - <<: *gpiopin
                   key: RX
                   target: "define:GWSERIAL_RX"
+                  mandatory: true
             - key: tx
               value: 1
               label: "TX"
@@ -176,6 +181,7 @@ types:
                 - <<: *gpiopin
                   key: TX
                   target: "define:GWSERIAL_TX"      
+                  mandatory: true
 resources:
   default: &esp32default
     serial: 2
diff --git a/webinstall/cibuild.js b/webinstall/cibuild.js
index 12829d2..976f550 100644
--- a/webinstall/cibuild.js
+++ b/webinstall/cibuild.js
@@ -270,9 +270,12 @@ class PipelineInfo{
                 }
             }    
         }
-        if (rt.target === undefined && typeof(parent) === 'object' && parent.target !== undefined){
+        if (rt.target === undefined && typeof(parent) === 'object'){
             rt.target=parent.target;
         }
+        if (rt.mandatory === undefined && typeof(parent) === 'object'){
+            rt.mandatory=parent.mandatory;
+        }
         return rt;
     }
     const expandList=(lst,parent)=>{
@@ -453,7 +456,13 @@ class PipelineInfo{
             for (let k in configStruct) {
                 let struct = configStruct[k];
                 if (round > 0) config[k] = struct.key;
-                if (struct.target !== undefined && struct.value !== undefined) {
+                if (struct.target !== undefined ) {
+                    if (struct.value === undefined){
+                        if (struct.mandatory && round > 0){
+                            errors+=" missing value for "+k+"\n";
+                        }
+                        continue;
+                    }
                     if (struct.target === 'environment' ) {
                         if (round > 0) environment = struct.value;
                         else allowedResources=struct.resource;