diff --git a/src/main/org/apache/tools/ant/helper/ProjectHelper2.java b/src/main/org/apache/tools/ant/helper/ProjectHelper2.java
index 68285d6dc..82be883ab 100644
--- a/src/main/org/apache/tools/ant/helper/ProjectHelper2.java
+++ b/src/main/org/apache/tools/ant/helper/ProjectHelper2.java
@@ -477,6 +477,11 @@ public class ProjectHelper2 extends ProjectHelper {
                 File file = new File(path);
                 if (!file.isAbsolute()) {
                     file = FILE_UTILS.resolveFile(context.getBuildFileParent(), path);
+                    context.getProject().log(
+                            "Warning: '" + systemId + "' in " + context.getBuildFile() +
+                            " should be expressed simply as '" + path.replace('\\', '/') +
+                            "' for compliance with other XML tools",
+                            Project.MSG_WARN);
                 }
                 context.getProject().log("file=" + file, Project.MSG_DEBUG);
                 try {
diff --git a/src/main/org/apache/tools/ant/helper/ProjectHelperImpl.java b/src/main/org/apache/tools/ant/helper/ProjectHelperImpl.java
index 8a7b45e57..3cd12f3ea 100644
--- a/src/main/org/apache/tools/ant/helper/ProjectHelperImpl.java
+++ b/src/main/org/apache/tools/ant/helper/ProjectHelperImpl.java
@@ -296,6 +296,11 @@ public class ProjectHelperImpl extends ProjectHelper {
                 File file = new File(path);
                 if (!file.isAbsolute()) {
                     file = FILE_UTILS.resolveFile(helperImpl.buildFileParent, path);
+                    helperImpl.project.log(
+                            "Warning: '" + systemId + "' in " + helperImpl.buildFile +
+                            " should be expressed simply as '" + path.replace('\\', '/') +
+                            "' for compliance with other XML tools",
+                            Project.MSG_WARN);
                 }
                 try {
                     InputSource inputSource = new InputSource(new FileInputStream(file));