diff --git a/_static/coalitions_demo.js b/_static/coalitions_demo.js
index 42253bb..f949e7d 100644
--- a/_static/coalitions_demo.js
+++ b/_static/coalitions_demo.js
@@ -46,7 +46,7 @@ exampleOffers = [
     {
         'offer_id': 3,
         'player': 1,
-        'members': [true, true, true],
+        'members': [true, true, false],
         'allocations': [80, 20, 0],
     },
     {
diff --git a/_static/live_bargaining.js b/_static/live_bargaining.js
index b72bf68..68558f5 100644
--- a/_static/live_bargaining.js
+++ b/_static/live_bargaining.js
@@ -47,7 +47,11 @@ openPopup = function (content, type) {
 for (let i = 0; i < numPlayers; i++) {
     isMemberCheckboxes[i].addEventListener('change', function () {
         allocationTextBoxes[i].disabled = !isMemberCheckboxes[i].checked;
-        allocationTextBoxes[i].value = 0;
+        if (!isMemberCheckboxes[i].checked) {
+            allocationTextBoxes[i].value = 0;
+        } else {
+            allocationTextBoxes[i].value = 1;
+        }
         updateTotalShareable();
         updateTotalShared();
         if (!allocationTextBoxes[i].disabled) {
@@ -56,12 +60,12 @@ for (let i = 0; i < numPlayers; i++) {
     });
 
     allocationTextBoxes[i].addEventListener('change', function () {
-        allocationTextBoxes[i].value = Math.floor(Math.max(0, allocationTextBoxes[i].value));
+        allocationTextBoxes[i].value = Math.floor(Math.max(1, allocationTextBoxes[i].value));
         updateTotalShared();
     });
     allocationTextBoxes[i].addEventListener("keyup", function (event) {
         if (event.key === "Enter") {
-            allocationTextBoxes[i].value = Math.floor(Math.max(0, allocationTextBoxes[i].value));
+            allocationTextBoxes[i].value = Math.floor(Math.max(1, allocationTextBoxes[i].value));
             updateTotalShared();
         }
     });
@@ -80,6 +84,12 @@ function sendOffer() {
         openPopup('Invalid proposal: total amount exceeds the budget available to this group', 'error');
         return;
     }
+    for (let i = 0; i < numPlayers; i++) {
+        if (isMemberCheckboxes[i].checked && allocationTextBoxes[i].value === '0') {
+            openPopup('Invalid proposal: all group members must receive a positive amount', 'error');
+            return;
+        }
+    }
     members = isMemberCheckboxes.map(member => member.checked);
     allocations = allocationTextBoxes.map(alloc => alloc.value);
     liveSend({ 'type': 'propose', 'members': members, 'allocations': allocations })
diff --git a/_static/proposal_demo.js b/_static/proposal_demo.js
index 8d98390..972ba39 100644
--- a/_static/proposal_demo.js
+++ b/_static/proposal_demo.js
@@ -59,7 +59,11 @@ openPopup = function (content, type) {
 for (let i = 0; i < numPlayers; i++) {
     isMemberCheckboxes[i].addEventListener('change', function () {
         allocationTextBoxes[i].disabled = !isMemberCheckboxes[i].checked;
-        allocationTextBoxes[i].value = 0;
+        if (!isMemberCheckboxes[i].checked) {
+            allocationTextBoxes[i].value = 0;
+        } else {
+            allocationTextBoxes[i].value = 1;
+        }
         updateTotalShareable();
         updateTotalShared();
         if (!allocationTextBoxes[i].disabled) {
@@ -68,12 +72,12 @@ for (let i = 0; i < numPlayers; i++) {
     });
 
     allocationTextBoxes[i].addEventListener('change', function () {
-        allocationTextBoxes[i].value = Math.floor(Math.max(0, allocationTextBoxes[i].value));
+        allocationTextBoxes[i].value = Math.floor(Math.max(1, allocationTextBoxes[i].value));
         updateTotalShared();
     });
     allocationTextBoxes[i].addEventListener("keyup", function (event) {
         if (event.key === "Enter") {
-            allocationTextBoxes[i].value = Math.floor(Math.max(0, allocationTextBoxes[i].value));
+            allocationTextBoxes[i].value = Math.floor(Math.max(1, allocationTextBoxes[i].value));
             updateTotalShared();
         }
     });
@@ -103,6 +107,12 @@ function sendOffer() {
         openPopup('Invalid proposal: total amount exceeds the budget available to this group', 'error');
         return;
     }
+    for (let i = 0; i < numPlayers; i++) {
+        if (isMemberCheckboxes[i].checked && allocationTextBoxes[i].value === '0') {
+            openPopup('Invalid proposal: all group members must receive a positive amount', 'error');
+            return;
+        }
+    }
 
     newPastOffers.push(newOffer);
     updatePastOffers(newPastOffers);
diff --git a/introduction/Coalitions.html b/introduction/Coalitions.html
index d57fa7b..890b897 100644
--- a/introduction/Coalitions.html
+++ b/introduction/Coalitions.html
@@ -22,7 +22,7 @@ <h4> Group formation </h4>
     Once the round ends, the final outcome and the payoffs of this round are determined as follows: 
     <span style="color: #b70505; font-weight: bold;"> 
         Only if <u> all players in a proposed group </u> agree on the same proposal is that proposal successful.
-        Note, that <u>players who are not included in a proposal do not have to agree to it</u>.
+        Note, that <u>players who are not included in a proposal (marked as "—") do not have to agree to it</u>.
     </span>
     The group is then successfully formed and its members' payoffs are then determined by the agreed-upon proposal. 
     All other players get 0. 
diff --git a/live_bargaining/__init__.py b/live_bargaining/__init__.py
index 3d856d9..0530c3a 100644
--- a/live_bargaining/__init__.py
+++ b/live_bargaining/__init__.py
@@ -220,6 +220,16 @@ def check_proposal_validity(player: Player, members, allocations):
             }
         }
 
+    if any(
+        member and allocation == 0 for member, allocation in zip(members, allocations)
+    ):
+        return {
+            player.id_in_group: {
+                "type": "error",
+                "content": "Invalid allocation: all members must receive a positive amount",  # noqa: E501
+            }
+        }
+
 
 def check_acceptance_validity(player: Player, offer_id):
     if not isinstance(offer_id, int):
diff --git a/live_bargaining/tests.py b/live_bargaining/tests.py
index cb99239..c9905ca 100644
--- a/live_bargaining/tests.py
+++ b/live_bargaining/tests.py
@@ -10,7 +10,7 @@ def create_offers(method, Y):
         {
             "type": "propose",
             "members": [True, True, True],
-            "allocations": [100, 0, 0],
+            "allocations": [90, 5, 5],
         },
     )
 
@@ -182,6 +182,24 @@ def test_invalid_input(method, Y, dummy_player, player_names):
         {3: {"type": "error", "content": "Data is incomplete"}},
     )
 
+    member_receives_zero = method(
+        1,
+        {
+            "type": "propose",
+            "members": [True, True, True],
+            "allocations": [100, 0, 0],
+        },
+    )
+    expect(
+        member_receives_zero,
+        {
+            1: {
+                "type": "error",
+                "content": "Invalid allocation: all members must receive a positive amount",
+            }
+        },
+    )
+
 
 def call_live_method(method, **kwargs):
     print(