diff --git a/jps/jps-builders-6/src/org/jetbrains/jps/PathUtils.java b/jps/jps-builders-6/src/org/jetbrains/jps/PathUtils.java
index 45a174a62ea9..a9c1e5d0185a 100644
--- a/jps/jps-builders-6/src/org/jetbrains/jps/PathUtils.java
+++ b/jps/jps-builders-6/src/org/jetbrains/jps/PathUtils.java
@@ -38,8 +38,8 @@ public class PathUtils {
 
   public static URI toURI(String localPath) {
     try {
-      final StringBuilder buf = new StringBuilder();
       final String p = FileUtilRt.toSystemIndependentName(localPath);
+      final StringBuilder buf = new StringBuilder(p.length() + 3);
       if (!p.startsWith("/")) {
         buf.append("///");
       }
diff --git a/jps/jps-builders-6/src/org/jetbrains/jps/javac/ZipFileObject.java b/jps/jps-builders-6/src/org/jetbrains/jps/javac/ZipFileObject.java
index d1375a0ff55e..e31f25243573 100644
--- a/jps/jps-builders-6/src/org/jetbrains/jps/javac/ZipFileObject.java
+++ b/jps/jps-builders-6/src/org/jetbrains/jps/javac/ZipFileObject.java
@@ -25,8 +25,8 @@ public class ZipFileObject extends JpsFileObject {
 
   @NotNull
   private static URI createUri(final File zipFile, String relPath) {
-    final StringBuilder buf = new StringBuilder();
     final String p = FileUtilRt.toSystemIndependentName(zipFile.getPath());
+    final StringBuilder buf = new StringBuilder(p.length() + relPath.length() + 5);
     if (!p.startsWith("/")) {
       buf.append("///");
     }