diff --git a/src/internet/model/ipv4-address-generator.cc b/src/internet/model/ipv4-address-generator.cc
index e6b6cf468..fb069c3c8 100644
--- a/src/internet/model/ipv4-address-generator.cc
+++ b/src/internet/model/ipv4-address-generator.cc
@@ -469,10 +469,10 @@ Ipv4AddressGeneratorImpl::IsAddressAllocated(const Ipv4Address address)
         {
             NS_LOG_LOGIC("Ipv4AddressGeneratorImpl::IsAddressAllocated(): Address Collision: "
                          << Ipv4Address(addr));
-            return false;
+            return true;
         }
     }
-    return true;
+    return false;
 }
 
 bool
diff --git a/src/internet/model/ipv6-address-generator.cc b/src/internet/model/ipv6-address-generator.cc
index c01efafda..a266895db 100644
--- a/src/internet/model/ipv6-address-generator.cc
+++ b/src/internet/model/ipv6-address-generator.cc
@@ -594,10 +594,10 @@ Ipv6AddressGeneratorImpl::IsAddressAllocated(const Ipv6Address address)
         {
             NS_LOG_LOGIC("Ipv6AddressGeneratorImpl::IsAddressAllocated(): Address Collision: "
                          << Ipv6Address(addr));
-            return false;
+            return true;
         }
     }
-    return true;
+    return false;
 }
 
 bool