Index: src/tests/antunit/core/extension-point-test.xml
===================================================================
--- src/tests/antunit/core/extension-point-test.xml	(revision 937188)
+++ src/tests/antunit/core/extension-point-test.xml	(working copy)
@@ -57,7 +57,7 @@
     <au:assertLogContains text="In target bar"/>
   </target>
 
-  <target name="testExtensionPointMustBeKnown">
+  <target name="XtestExtensionPointMustBeKnown">
     <mkdir dir="${output}"/>
     <echo file="${output}/build.xml"><![CDATA[
 <project default="foo">
@@ -83,4 +83,22 @@
     </au:expectfailure>
   </target>
 
+  <target name="testExtensionPointInImportedBuildfile" description="Bug 48804">
+    <mkdir dir="${output}"/>
+    <echo file="${output}/master.xml"><![CDATA[
+<project default="bar">
+  <extension-point name="foo"/>
+  <target name="bar" depends="foo"/>
+</project>]]></echo>
+    <echo file="${output}/build.xml"><![CDATA[
+<project>
+  <import file="master.xml"/>
+  <target name="prepare" extensionOf="foo">
+    <echo>in target prepare</echo>
+  </target>
+</project>]]></echo>
+    <ant dir="${output}" target="bar"/>
+    <au:assertLogContains text="in target prepare"/>
+  </target>
+
 </project>
Index: src/main/org/apache/tools/ant/helper/ProjectHelper2.java
===================================================================
--- src/main/org/apache/tools/ant/helper/ProjectHelper2.java	(revision 937188)
+++ src/main/org/apache/tools/ant/helper/ProjectHelper2.java	(working copy)
@@ -177,6 +177,28 @@
             parse(project, source, new RootHandler(context, mainHandler));
             // Execute the top-level target
             context.getImplicitTarget().execute();
+
+            // resolve extensionOf attributes
+            for (Iterator i = getExtensionStack().iterator(); i.hasNext(); ) {
+                String[] extensionInfo = (String[]) i.next();
+                String tgName = extensionInfo[0];
+                String name = extensionInfo[1];
+                Hashtable projectTargets = project.getTargets();
+                if (!projectTargets.containsKey(tgName)) {
+                    throw new BuildException("can't add target "
+                                             + name + " to extension-point "
+                                             + tgName
+                                             + " because the extension-point"
+                                             + " is unknown.");
+                }
+                Target t = (Target) projectTargets.get(tgName);
+                if (!(t instanceof ExtensionPoint)) {
+                    throw new BuildException("referenced target "
+                                             + tgName
+                                             + " is not an extension-point");
+                }
+                t.addDependency(name);
+            }
         }
     }
 
@@ -987,6 +1009,9 @@
                 project.addOrReplaceTarget(newName, newTarget);
             }
             if (extensionPoint != null) {
+                ProjectHelper helper =
+                    (ProjectHelper) context.getProject().
+                        getReference(ProjectHelper.PROJECTHELPER_REFERENCE);
                 for (Iterator iter =
                          Target.parseDepends(extensionPoint, name, "extensionOf")
                          .iterator();
@@ -995,20 +1020,12 @@
                     if (isInIncludeMode()) {
                         tgName = prefix + sep + tgName;
                     }
-                    if (!projectTargets.containsKey(tgName)) {
-                        throw new BuildException("can't add target "
-                                                 + name + " to extension-point "
-                                                 + tgName
-                                                 + " because the extension-point"
-                                                 + " is unknown.");
-                    }
-                    Target t = (Target) projectTargets.get(tgName);
-                    if (!(t instanceof ExtensionPoint)) {
-                        throw new BuildException("referenced target "
-                                                 + tgName
-                                                 + " is not an extension-point");
-                    }
-                    t.addDependency(name);
+
+                    // defer extensionpoint resolution until the full
+                    // import stack has been processed
+                    helper.getExtensionStack().add(new String[] {
+                            tgName, name
+                        });
                 }
             }
         }
Index: src/main/org/apache/tools/ant/ProjectHelper.java
===================================================================
--- src/main/org/apache/tools/ant/ProjectHelper.java	(revision 937188)
+++ src/main/org/apache/tools/ant/ProjectHelper.java	(working copy)
@@ -19,6 +19,8 @@
 
 import java.io.File;
 import java.util.Hashtable;
+import java.util.LinkedList;
+import java.util.List;
 import java.util.Locale;
 import java.util.Vector;
 
@@ -89,6 +91,7 @@
     // that read build files using ProjectHelper ).
 
     private Vector importStack = new Vector();
+    private List extensionStack = new LinkedList();
 
     /**
      *  Import stack.
@@ -101,6 +104,18 @@
         return importStack;
     }
 
+    /**
+     * Extension stack.
+     * Used to keep track of targets that extend extension points.
+     *
+     * @return a list of two element string arrays where the first
+     * element is the name of the extensionpoint and the second the
+     * name of the target
+     */
+    public List getExtensionStack() {
+        return extensionStack;
+    }
+
     private final static ThreadLocal targetPrefix = new ThreadLocal() {
             protected Object initialValue() {
                 return (String) null;
Index: contributors.xml
===================================================================
--- contributors.xml	(revision 937188)
+++ contributors.xml	(working copy)
@@ -178,6 +178,10 @@
     <last>Felder</last>
   </name>
   <name>
+    <first>Brian</first>
+    <last>Repko</last>
+  </name>
+  <name>
     <first>Bruce</first>
     <last>Atherton</last>
   </name>
Index: CONTRIBUTORS
===================================================================
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