diff --git a/checker/comprog b/checker/comprog
index 2f0bb2e..2715d50 100755
--- a/checker/comprog
+++ b/checker/comprog
@@ -19,7 +19,7 @@ case _"$LANG" in
         
     _C)
         ulimit -f 1000
-        gcc -std=c99 -g -o prog $@
+        gcc -std=c99 -g -o prog -lm $@
         ;;
 
     _Cpp)
diff --git a/checker/interleaveio.py b/checker/interleaveio.py
index c742d17..d40b2bb 100755
--- a/checker/interleaveio.py
+++ b/checker/interleaveio.py
@@ -30,11 +30,12 @@ def readAvailable(p, fd, delay):
             done = True
       if not done :
          if p.poll() == None :
-            time.sleep(0.1)
             if delay :
+               time.sleep(0.1)
                if time.time() >= start + timeout :
                   done = True
             else :
+               time.sleep(0.01)               
                iters -= 1
                if (iters <= 0) :
                   done = True
diff --git a/checker/src/com/horstmann/codecheck/CLanguage.java b/checker/src/com/horstmann/codecheck/CLanguage.java
index 281183e..cd87366 100644
--- a/checker/src/com/horstmann/codecheck/CLanguage.java
+++ b/checker/src/com/horstmann/codecheck/CLanguage.java
@@ -17,7 +17,7 @@ public String getExtension() {
     @Override
     public boolean isSource(Path p) {
         String name = p.toString();
-        return name.endsWith(".c") || name.endsWith(".h");
+        return name.endsWith(".c") || name.endsWith(".h") || name.endsWith(".s") || name.endsWith(".S");
     }
     
     private static Pattern mainPattern = Pattern.compile("\\s*((int|void)\\s+)?main\\s*\\([^)]*\\)\\s*(\\{\\s*)?");
diff --git a/checker/src/com/horstmann/codecheck/Main.java b/checker/src/com/horstmann/codecheck/Main.java
index 3b081ef..367eb99 100644
--- a/checker/src/com/horstmann/codecheck/Main.java
+++ b/checker/src/com/horstmann/codecheck/Main.java
@@ -633,7 +633,7 @@ else if (System.getProperty("com.horstmann.codecheck.codioreport") != null)
             // the supplied files that the students are entitled to see
             Set<Path> printFiles = Util.filterNot(useFiles, "test*.in", "test*.out", "Input", 
                     "*.png", "*.PNG", "*.gif", "*.GIF", "*.jpg", "*.jpeg", "*.JPG", 
-                    "*.jar");      
+                    "*.jar", "*.pdf");      
 
             printFiles.removeAll(annotations.getHidden());