diff --git a/src/variable.cpp b/src/variable.cpp
index a564847b68..979b0e4c64 100644
--- a/src/variable.cpp
+++ b/src/variable.cpp
@@ -4354,9 +4354,13 @@ int Variable::special_function(char *word, char *contents, Tree **tree, Tree **t
     } else argstack[nargstack++] = value;
 
   } else if (strcmp(word,"extract_setting") == 0) {
-    if (narg != 1) print_var_error(FLERR,"Invalid extract_setting() function in variable formula",ivar);
+    if (narg != 1) print_var_error(FLERR,"Invalid extract_setting() function syntax in variable formula",ivar);
 
     value = lammps_extract_setting(lmp, args[0]);
+    if (value < 0) {
+      auto mesg = fmt::format("Unknown setting {} for extract_setting() function in variable formula",args[0]);
+      print_var_error(FLERR,mesg,ivar);
+    }
 
     // save value in tree or on argstack
 
diff --git a/unittest/commands/test_variables.cpp b/unittest/commands/test_variables.cpp
index cf124eeafd..60a9f44095 100644
--- a/unittest/commands/test_variables.cpp
+++ b/unittest/commands/test_variables.cpp
@@ -380,6 +380,7 @@ TEST_F(VariableTest, Functions)
     command("variable ten1   equal     tan(v_eight/2.0)");
     command("variable ten2   equal     asin(-1.0)+acos(0.0)");
     command("variable ten3   equal     floor(100*random(0.2,0.8,v_seed)+1)");
+    command("variable ten4   equal     extract_setting(world_size)");
     END_HIDE_OUTPUT();
 
     ASSERT_GT(variable->compute_equal(variable->find("two")), 0.99);
@@ -393,9 +394,18 @@ TEST_F(VariableTest, Functions)
     ASSERT_FLOAT_EQ(variable->compute_equal(variable->find("ten1")), 1);
     ASSERT_GT(variable->compute_equal(variable->find("ten3")), 19);
     ASSERT_LT(variable->compute_equal(variable->find("ten3")), 81);
+    ASSERT_DOUBLE_EQ(variable->compute_equal(variable->find("ten4")), 1);
 
     TEST_FAILURE(".*ERROR: Variable four: Invalid syntax in variable formula.*",
                  command("print \"${four}\""););
+    TEST_FAILURE(".*ERROR on proc 0: Invalid immediate variable.*",
+                 command("print \"$(extract_setting()\""););
+    TEST_FAILURE(".*ERROR on proc 0: Invalid immediate variable.*",
+                 command("print \"$(extract_setting()\""););
+    TEST_FAILURE(".*ERROR: Invalid extract_setting.. function syntax in variable formula.*",
+                 command("print \"$(extract_setting(one,two))\""););
+    TEST_FAILURE(".*ERROR: Unknown setting nprocs for extract_setting.. function in variable formula.*",
+                 command("print \"$(extract_setting(nprocs))\""););
 }
 
 TEST_F(VariableTest, IfCommand)