diff --git a/compiler/AST/AggregateType.cpp b/compiler/AST/AggregateType.cpp
index d8b84a474415..a743f83f4dbe 100644
--- a/compiler/AST/AggregateType.cpp
+++ b/compiler/AST/AggregateType.cpp
@@ -2297,7 +2297,8 @@ void AggregateType::buildDefaultInitializer() {
       } else {
         USR_FATAL(this, "Unable to generate initializer for type '%s'", this->symbol->name);
       }
-    } else {
+    } else {  // Handle unions
+      /* 0-arg initializer */
       DefExpr* def = new DefExpr(fn);
       symbol->defPoint->insertBefore(def);
 
@@ -2311,6 +2312,91 @@ void AggregateType::buildDefaultInitializer() {
       normalize(fn);
 
       methods.add(fn);
+
+      /* 1-arg initializers */
+      for_fields(fieldDefExpr, this) {
+        SET_LINENO(this);
+        FnSymbol* fn = new FnSymbol("init");
+        fn->cname = fn->name;
+
+        fn->addFlag(FLAG_COMPILER_GENERATED);
+        fn->addFlag(FLAG_LAST_RESORT);
+        fn->addFlag(FLAG_SUPPRESS_LVALUE_ERRORS);
+
+        ArgSymbol* _mt = new ArgSymbol(INTENT_BLANK, "_mt", dtMethodToken);
+        fn->insertFormalAtTail(_mt);
+
+        ArgSymbol* _this = new ArgSymbol(INTENT_BLANK, "this", this);
+        fn->_this = _this;
+        _this->addFlag(FLAG_ARG_THIS);
+        fn->insertFormalAtTail(_this);
+
+        fn->insertAtTail(new CallExpr(PRIM_SET_UNION_ID,
+                                      fn->_this,
+                                      new_IntSymbol(-1)));
+
+        {
+          SET_LINENO(fieldDefExpr);
+          VarSymbol* field = toVarSymbol(fieldDefExpr);
+          if (!field) {
+            INT_FATAL("unexpected: fieldDefExpr can't be made a VarSymbol");
+          }
+          assert(!field->hasFlag(FLAG_SUPER_CLASS));
+
+          DefExpr* defPoint = field->defPoint;
+          const char* name = field->name;
+          ArgSymbol* arg = new ArgSymbol(INTENT_IN, name, dtUnknown);
+
+          if (field->hasEitherFlag(FLAG_TYPE_VARIABLE, FLAG_PARAM)) {
+            USR_FATAL(arg, "union types don't currently support `type` or `param` fields");
+          }
+
+          {
+            SET_LINENO(field);
+
+            if (field->hasFlag(FLAG_UNSAFE))
+              arg->addFlag(FLAG_UNSAFE);
+
+            // TODO: We should really do this somewhere else, and let this
+            // method focus on the initializer and not modify the type's fields.
+            if (LoopExpr* fe = toLoopExpr(defPoint->init)) {
+              if (field->isType() == false) {
+                if (defPoint->exprType == NULL) {
+                  CallExpr* copy = new CallExpr(astr_initCopy);
+                  defPoint->init->replace(copy);
+
+                  Symbol *definedConst = defPoint->sym->hasFlag(FLAG_CONST) ?
+                                           gTrue : gFalse;
+                  copy->insertAtTail(fe);
+                  copy->insertAtTail(definedConst);
+                }
+              }
+            }
+
+            if (defPoint->exprType == NULL) {
+              USR_FATAL(field, "currently, union fields must have a declared type");
+            } else if (defPoint->init == NULL) {
+              fieldToArgType(defPoint, arg);
+            } else {
+              USR_FATAL(field, "currently, union fields cannot have initializer expressions");
+            }
+            fn->insertFormalAtTail(arg);
+            fn->insertAtTail(new CallExpr("=", new CallExpr(".",
+                                                            fn->_this,
+                                                            new_CStringSymbol(name)),
+                                          arg));
+          }
+        }
+
+        DefExpr* def = new DefExpr(fn);
+        symbol->defPoint->insertBefore(def);
+        fn->setMethod(true);
+        fn->addFlag(FLAG_METHOD_PRIMARY);
+        preNormalizeInitMethod(fn);
+        normalize(fn);
+        checkUseBeforeDefs(fn);
+        methods.add(fn);
+      }
     }
 
     builtDefaultInit = true;
@@ -3141,6 +3227,14 @@ void AggregateType::setCreationStyle(TypeSymbol* t, FnSymbol* fn) {
       USR_FATAL(fn, "an initializer cannot be declared without parentheses");
     }
 
+    // For a user-defined union initializer to work properly, the active
+    // field indicator must be initialized to -1
+    if (ct->isUnion()) {
+      fn->insertAtHead(new CallExpr(PRIM_SET_UNION_ID,
+                                    fn->_this,
+                                    new_IntSymbol(-1)));
+    }
+
     if (ct->hasUserDefinedInit == false) {
       // We hadn't previously seen an initializer definition.
       // Update the field on the type appropriately.
diff --git a/test/classes/diten/constructUnion.bad b/test/classes/diten/constructUnion.bad
deleted file mode 100644
index 6bb558ddd45d..000000000000
--- a/test/classes/diten/constructUnion.bad
+++ /dev/null
@@ -1,4 +0,0 @@
-constructUnion.chpl:6: error: unresolved call 'IntOrReal.init(i=1)'
-constructUnion.chpl:1: note: this candidate did not match: IntOrReal.init()
-constructUnion.chpl:6: note: because call uses named argument i
-constructUnion.chpl:1: note: but function contains no formal named i
diff --git a/test/classes/diten/constructUnion.future b/test/classes/diten/constructUnion.future
deleted file mode 100644
index 0775dfe15625..000000000000
--- a/test/classes/diten/constructUnion.future
+++ /dev/null
@@ -1,2 +0,0 @@
-design: union should be initializable with a single field
-#15189
diff --git a/test/library/standard/Reflection/field-queries-ok.chpl b/test/library/standard/Reflection/field-queries-ok.chpl
index 1769d1a3b3d1..0fe8a089a80f 100644
--- a/test/library/standard/Reflection/field-queries-ok.chpl
+++ b/test/library/standard/Reflection/field-queries-ok.chpl
@@ -64,11 +64,4 @@ union UCon {
 test(UCon);
 
 
-union UGen {
-  var f1, f2, f3, f4, f5, f6;
-}
-
-test(UGen(?));
-
-
 compilerError("=== done ===");
diff --git a/test/library/standard/Reflection/field-queries-ok.good b/test/library/standard/Reflection/field-queries-ok.good
index 4c97145879d6..ec09d27c8996 100644
--- a/test/library/standard/Reflection/field-queries-ok.good
+++ b/test/library/standard/Reflection/field-queries-ok.good
@@ -145,11 +145,4 @@ field-queries-ok.chpl:64: warning:   hasField        true
 field-queries-ok.chpl:64: warning:   getFieldIndex   5
 field-queries-ok.chpl:64: warning:   isFieldBound 5  true
 field-queries-ok.chpl:64: warning:   isFieldBound f6 true
-field-queries-ok.chpl:71: warning: ===== UGen
-field-queries-ok.chpl:71: warning:   getNumFields    6
-field-queries-ok.chpl:71: warning:   getFieldName    f6
-field-queries-ok.chpl:71: warning:   hasField        true
-field-queries-ok.chpl:71: warning:   getFieldIndex   5
-field-queries-ok.chpl:71: warning:   isFieldBound 5  false
-field-queries-ok.chpl:71: warning:   isFieldBound f6 false
-field-queries-ok.chpl:74: error: === done ===
+field-queries-ok.chpl:67: error: === done ===
diff --git a/test/types/unions/union-compgen-init.chpl b/test/types/unions/union-compgen-init.chpl
new file mode 100644
index 000000000000..4891633d904d
--- /dev/null
+++ b/test/types/unions/union-compgen-init.chpl
@@ -0,0 +1,18 @@
+union u {
+  var w: int;
+  var x: int;
+  var y: real;
+  var z: string;
+}
+
+var u0 = new u(),
+    u1 = new u(w=45),
+    u2 = new u(x=78),
+    u3 = new u(y=33.3),
+    u4 = new u(z="hi");
+
+writeln(u0);
+writeln(u1);
+writeln(u2);
+writeln(u3);
+writeln(u4);
diff --git a/test/types/unions/union-compgen-init.good b/test/types/unions/union-compgen-init.good
new file mode 100644
index 000000000000..916c37bf17b3
--- /dev/null
+++ b/test/types/unions/union-compgen-init.good
@@ -0,0 +1,5 @@
+()
+(w = 45)
+(x = 78)
+(y = 33.3)
+(z = hi)
diff --git a/test/types/unions/union-init1.good b/test/types/unions/union-init1.good
index 758ff5464b69..1260bc9e8962 100644
--- a/test/types/unions/union-init1.good
+++ b/test/types/unions/union-init1.good
@@ -3,3 +3,6 @@ union-init1.chpl:7: error: unresolved call 'U.init(x=1, y=20.0)'
 union-init1.chpl:1: note: this candidate did not match: U.init()
 union-init1.chpl:7: note: because call uses named argument x
 union-init1.chpl:1: note: but function contains no formal named x
+union-init1.chpl:7: note: other candidates are:
+union-init1.chpl:1: note:   U.init(x: int(64))
+union-init1.chpl:1: note:   U.init(y: real(64))
diff --git a/test/types/unions/union-init2.bad b/test/types/unions/union-init2.bad
deleted file mode 100644
index da5f245419e4..000000000000
--- a/test/types/unions/union-init2.bad
+++ /dev/null
@@ -1,5 +0,0 @@
-union-init2.chpl:6: In function 'main':
-union-init2.chpl:7: error: unresolved call 'U.init(y=20.0)'
-union-init2.chpl:1: note: this candidate did not match: U.init()
-union-init2.chpl:7: note: because call uses named argument y
-union-init2.chpl:1: note: but function contains no formal named y
diff --git a/test/types/unions/union-init2.future b/test/types/unions/union-init2.future
deleted file mode 100644
index 0775dfe15625..000000000000
--- a/test/types/unions/union-init2.future
+++ /dev/null
@@ -1,2 +0,0 @@
-design: union should be initializable with a single field
-#15189
diff --git a/test/types/unions/union-init3.future b/test/types/unions/union-init3.future
deleted file mode 100644
index a8880a23ada8..000000000000
--- a/test/types/unions/union-init3.future
+++ /dev/null
@@ -1,2 +0,0 @@
-design: should be able to write single arg initializer for union
-#15189
diff --git a/test/types/unions/union-init3.skipif b/test/types/unions/union-init3.skipif
deleted file mode 100644
index 393ecc867dde..000000000000
--- a/test/types/unions/union-init3.skipif
+++ /dev/null
@@ -1 +0,0 @@
-CHPL_TEST_VGRND_EXE != on
diff --git a/test/types/unions/union-typelessField.chpl b/test/types/unions/union-typelessField.chpl
new file mode 100644
index 000000000000..cf3bce506a87
--- /dev/null
+++ b/test/types/unions/union-typelessField.chpl
@@ -0,0 +1,9 @@
+union u {
+  var x, y, z;
+}
+
+var myU: u;
+myU.x = 42;
+writeln(myU);
+myU.y = "hi";
+
diff --git a/test/types/unions/union-typelessField.good b/test/types/unions/union-typelessField.good
new file mode 100644
index 000000000000..64f9dea6843b
--- /dev/null
+++ b/test/types/unions/union-typelessField.good
@@ -0,0 +1 @@
+union-typelessField.chpl:2: error: currently, union fields must have a declared type
diff --git a/test/types/unions/union-typelessField2.chpl b/test/types/unions/union-typelessField2.chpl
new file mode 100644
index 000000000000..4945f914c915
--- /dev/null
+++ b/test/types/unions/union-typelessField2.chpl
@@ -0,0 +1,11 @@
+union u {
+  var x;
+  var y;
+  var z;
+}
+
+var myU: u;
+myU.x = 42;
+writeln(myU);
+myU.y = "hi";
+
diff --git a/test/types/unions/union-typelessField2.good b/test/types/unions/union-typelessField2.good
new file mode 100644
index 000000000000..dfffabd5d04c
--- /dev/null
+++ b/test/types/unions/union-typelessField2.good
@@ -0,0 +1,3 @@
+union-typelessField2.chpl:2: error: union fields must have an explicit type
+union-typelessField2.chpl:3: error: union fields must have an explicit type
+union-typelessField2.chpl:4: error: union fields must have an explicit type