diff --git a/compiler/macroexpander.stanza b/compiler/macroexpander.stanza
index 35abc0391..0e2cde426 100644
--- a/compiler/macroexpander.stanza
+++ b/compiler/macroexpander.stanza
@@ -76,33 +76,28 @@ public defn StanzaMacroexpander () -> StanzaMacroexpander :
     ;Main algorithm
     label<MacroPlugin|False|MissingPackages> return :
 
-      ;Find the loaded macro
-      val lm = find-loaded-macro()
-
-      ;Return the loaded macro if one was found, and
-      ;it was from a file.
-      match(lm:LoadedMacros) :
-        if source(lm) == LoadedFromFile :
-          return(plugin(lm))
-
-      ;Check whether the root expander supports it.
-      if supported-by-root?() :
-        return(false)
-
-      ;Now check whether a loaded already supports it.
-      match(lm:LoadedMacros) :
-        return(plugin(lm))
+      ;Find an already loaded macro.
+      match(find-loaded-macro()) :
+        (lm:LoadedMacros) : return(plugin(lm))
+        (f:False) : false
 
       ;Now see whether a plugin can be found via the proj file.
       match(find-using-proj()) :
         (p:MacroPlugin) : return(p)
         (f:False) : false
+
+      ;Check whether the root expander supports it.
+      if supported-by-root?() :
+        return(false)
         
       ;Failed to find an appropriate support, return an error.
       compute-error()
 
   ;Convenience: Use the names as the overlays.
   ;Assume that the base is `core.
+  ;Returns MacroPlugin if the packages are found in a plugin.
+  ;Returns False if the packages have built-in support.
+  ;Returns MissingPackages if the packages are not found.
   defn find-plugin (overlays:Overlays) -> MacroPlugin|False|MissingPackages :
     if base(overlays) != `core :
       fatal("Expected base package is core.")
diff --git a/compiler/params.stanza b/compiler/params.stanza
index 5c6f28f94..329799d33 100644
--- a/compiler/params.stanza
+++ b/compiler/params.stanza
@@ -18,7 +18,7 @@ public defn compiler-flags () :
   to-tuple(COMPILE-FLAGS)
 
 ;========= Stanza Configuration ========
-public val STANZA-VERSION = [0 17 44]
+public val STANZA-VERSION = [0 17 45]
 public var STANZA-INSTALL-DIR:String = ""
 public var OUTPUT-PLATFORM:Symbol = `platform
 public var STANZA-PKG-DIRS:List<String> = List()
diff --git a/compiler/proj-utils.stanza b/compiler/proj-utils.stanza
index 47a00ce27..46f8f6462 100644
--- a/compiler/proj-utils.stanza
+++ b/compiler/proj-utils.stanza
@@ -123,12 +123,11 @@ defn main-items (return:ProjItem -> ?, s:ProjStmt) -> ? :
     (s:ImportWhenStmt) :
       return(main-item(s))
       for d in dependencies(s) do : return(PackageItem(d))
-    ;Build statements are never relevant.
-    (s:BuildStmt) :
-      false
+    ;Never relevant
+    (s:BuildStmt) : false
+    (s:SyntaxPackagesDefinedInStmt) : false
     ;All other statements only have one main item.
-    (s:ProjStmt) :
-      return(main-item(s))
+    (s:ProjStmt) : return(main-item(s))
 
 ;The main-item of a statement is used to match one
 ;statement against another when comparing isolates.
@@ -137,11 +136,11 @@ defn main-item (s:ProjStmt) -> ProjItem :
     (s:DefinedInStmt) : PackageItem(package(s))
     (s:RequiresStmt) : PackageItem(package(s))
     (s:ImportWhenStmt) : PackageItem(package(s))
-    (s:CompileStmt) :
+    (s:CompileStmt) : 
       if file?(s) : CCFileItem(name(s) as String)
       else : CCFlagItem(name(s))
-    (s:ForeignPackageParamsStmt) :
-      PackageManagerItem(package-manager(s))
+    (s:ForeignPackageParamsStmt) : PackageManagerItem(package-manager(s))
+    (s:PackagesDefinedInStmt) : PackagePrefixItem(packages(s))
   
 ;------------------------------------------------------------
 ;-------------------- ProjItem Utility ----------------------
@@ -179,6 +178,13 @@ with:
   equalable => true
   hashable => true
 
+;Represents the prefix used by a PackagesDefinedInStmt.
+defstruct PackagePrefixItem <: ProjItem :
+  packages:Symbol|False
+with:
+  equalable => true
+  hashable => true
+
 ;============================================================
 ;==================== Package Tree ==========================
 ;============================================================
@@ -240,6 +246,7 @@ defn type-tag (s:ProjStmt) -> Int :
     (s:ImportWhenStmt) : 2
     (s:CompileStmt) : 3
     (s:ForeignPackageParamsStmt) : 4
+    (s:PackagesDefinedInStmt) : 5
 
 ;Return true if two extracted isolates are equal to each other.
 public defn isomorphic? (a:ProjIsolate, b:ProjIsolate) -> True|False :
diff --git a/compiler/repl.stanza b/compiler/repl.stanza
index 8da99fabb..c5c90fbac 100644
--- a/compiler/repl.stanza
+++ b/compiler/repl.stanza
@@ -245,8 +245,6 @@ defn prompter (style:TerminalStyle, prompt:String, continue:String) -> Prompter
 ;============================================================
 public val REPL-INITIAL-SYNTAX-PACKAGES = Vector<Symbol>()
 public defn register-initial-repl-syntax (name:Symbol) :
-  if not syntax-package-exists?(name) :
-    fatal("No syntax package called %_." % [name])
   add(REPL-INITIAL-SYNTAX-PACKAGES, name)
 
 ;============================================================