diff --git a/nixos/modules/services/cluster/hadoop/hdfs.nix b/nixos/modules/services/cluster/hadoop/hdfs.nix
index 6c185b9cd245..75a97e535479 100644
--- a/nixos/modules/services/cluster/hadoop/hdfs.nix
+++ b/nixos/modules/services/cluster/hadoop/hdfs.nix
@@ -158,8 +158,8 @@ in
         50010 # datanode.address
         50020 # datanode.ipc.address
       ];
-      extraConfig.services.hadoop.hdfsSiteInternal."dfs.datanode.data.dir" = let d = cfg.hdfs.datanode.dataDirs; in
-        if (d!= null) then (concatMapStringsSep "," (x: "["+x.type+"]file://"+x.path) cfg.hdfs.datanode.dataDirs) else d;
+      extraConfig.services.hadoop.hdfsSiteInternal."dfs.datanode.data.dir" = mkIf (cfg.hdfs.datanode.dataDirs!= null)
+        (concatMapStringsSep "," (x: "["+x.type+"]file://"+x.path) cfg.hdfs.datanode.dataDirs);
     })
 
     (hadoopServiceConfig {
diff --git a/nixos/modules/services/cluster/hadoop/yarn.nix b/nixos/modules/services/cluster/hadoop/yarn.nix
index 0a03fe6dab69..be0b9c13cd35 100644
--- a/nixos/modules/services/cluster/hadoop/yarn.nix
+++ b/nixos/modules/services/cluster/hadoop/yarn.nix
@@ -178,18 +178,18 @@ in
 
       services.hadoop.gatewayRole.enable = true;
 
-      services.hadoop.yarnSiteInternal = with cfg.yarn.nodemanager; {
-        "yarn.nodemanager.local-dirs" = localDir;
+      services.hadoop.yarnSiteInternal = with cfg.yarn.nodemanager; mkMerge [ ({
+        "yarn.nodemanager.local-dirs" = mkIf (localDir!= null) (concatStringsSep "," localDir);
         "yarn.scheduler.maximum-allocation-vcores" = resource.maximumAllocationVCores;
         "yarn.scheduler.maximum-allocation-mb" = resource.maximumAllocationMB;
         "yarn.nodemanager.resource.cpu-vcores" = resource.cpuVCores;
         "yarn.nodemanager.resource.memory-mb" = resource.memoryMB;
-      } // mkIf useCGroups {
+      }) (mkIf useCGroups {
         "yarn.nodemanager.linux-container-executor.cgroups.hierarchy" = "/hadoop-yarn";
         "yarn.nodemanager.linux-container-executor.resources-handler.class" = "org.apache.hadoop.yarn.server.nodemanager.util.CgroupsLCEResourcesHandler";
         "yarn.nodemanager.linux-container-executor.cgroups.mount" = "true";
         "yarn.nodemanager.linux-container-executor.cgroups.mount-path" = "/run/wrappers/yarn-nodemanager/cgroup";
-      };
+      })];
 
       networking.firewall.allowedTCPPortRanges = [
         (mkIf (cfg.yarn.nodemanager.openFirewall) {from = 1024; to = 65535;})
diff --git a/nixos/tests/hadoop/yarn.nix b/nixos/tests/hadoop/yarn.nix
index 1bf8e3831f67..08c8ff857d8c 100644
--- a/nixos/tests/hadoop/yarn.nix
+++ b/nixos/tests/hadoop/yarn.nix
@@ -19,7 +19,7 @@ import ../make-test-python.nix ({ package, ... }: {
           enable = true;
           openFirewall = true;
         };
-        yarnSite = options.services.hadoop.yarnSite.default // {
+        yarnSite = {
           "yarn.resourcemanager.hostname" = "resourcemanager";
           "yarn.nodemanager.log-dirs" = "/tmp/userlogs";
         };