diff --git a/src/base/trie.hh b/src/base/trie.hh
index e6b2881..1d110b4 100644
--- a/src/base/trie.hh
+++ b/src/base/trie.hh
@@ -185,6 +185,10 @@
     Handle
     insert(Key key, unsigned width, Value *val)
     {
+        // We use NULL value pointers to mark internal nodes of the trie, so
+        // we don't allow inserting them as real values.
+        assert(val);
+
         // Build a mask which masks off all the bits we don't care about.
         Key new_mask = ~(Key)0;
         if (width < MaxBits)
diff --git a/src/unittest/trietest.cc b/src/unittest/trietest.cc
index 7abef4c..12d434f 100644
--- a/src/unittest/trietest.cc
+++ b/src/unittest/trietest.cc
@@ -30,7 +30,6 @@
 
 #include <iostream>
 
-#include "base/cprintf.hh"
 #include "base/trie.hh"
 #include "base/types.hh"
 #include "unittest/unittest.hh"
@@ -54,33 +53,33 @@
     // Create an empty Ptr and verify it's data pointer is NULL.
     setCase("An empty trie.");
     TestTrie trie1;
-    trie1.dump("Empty");
-    cprintf("\n\n");
+    EXPECT_EQ(trie1.lookup(0x123456701234567), NULL);
 
     setCase("A single entry.");
     trie1.insert(0x0123456789abcdef, 40, ptr(1));
-    trie1.dump("One entry");
-    cprintf("\n\n");
+    EXPECT_EQ(trie1.lookup(0x123456701234567), NULL);
+    EXPECT_EQ(trie1.lookup(0x123456789ab0000), ptr(1));
 
     setCase("Two entries, one on the way to the other.");
     TestTrie trie2;
     trie2.insert(0x0123456789abcdef, 40, ptr(1));
     trie2.insert(0x0123456789abcdef, 36, ptr(2));
-    trie2.dump("Two entries inline v1");
-    cprintf("\n\n");
+    EXPECT_EQ(trie2.lookup(0x123456700000000), NULL);
+    EXPECT_EQ(trie2.lookup(0x123456789ab0000), ptr(2));
 
     TestTrie trie3;
     trie3.insert(0x0123456789abcdef, 36, ptr(2));
     trie3.insert(0x0123456789abcdef, 40, ptr(1));
-    trie3.dump("Two entries inline v2");
-    cprintf("\n\n");
+    EXPECT_EQ(trie3.lookup(0x123456700000000), NULL);
+    EXPECT_EQ(trie3.lookup(0x123456789ab0000), ptr(2));
 
     setCase("Two entries on different paths.");
     TestTrie trie4;
     trie4.insert(0x0123456789abcdef, 40, ptr(2));
     trie4.insert(0x0123456776543210, 40, ptr(1));
-    trie4.dump("Two split entries");
-    cprintf("\n\n");
+    EXPECT_EQ(trie4.lookup(0x0123456789000000), ptr(2));
+    EXPECT_EQ(trie4.lookup(0x0123456776000000), ptr(1));
+    EXPECT_EQ(trie4.lookup(0x0123456700000000), NULL);
 
     setCase("Skipping past an entry but not two.");
     TestTrie trie5;
@@ -88,8 +87,6 @@
     trie5.insert(0x0123000000000000, 40, ptr(1));
     trie5.insert(0x0123456780000000, 40, ptr(3));
     trie5.insert(0x0123456700000000, 40, ptr(2));
-    trie5.dump("Complex insertion");
-    cprintf("\n\n");
 
     setCase("Looking things up.");
     EXPECT_EQ(trie5.lookup(0x0123000000000000), ptr(1));
@@ -105,8 +102,6 @@
     trie6.insert(0x0123456780000000, 40, ptr(3));
     node1 = trie6.insert(0x0123456700000000, 40, ptr(2));
     node2 = trie6.insert(0x0123456700000000, 32, ptr(10));
-    trie6.dump("Fill before removal");
-    cprintf("\n\n");
 
     EXPECT_EQ(trie6.lookup(0x0123000000000000), ptr(1));
     EXPECT_EQ(trie6.lookup(0x0123456700000000), ptr(10));
@@ -114,8 +109,6 @@
     EXPECT_EQ(trie6.lookup(0x0123456789000000), ptr(10));
 
     trie6.remove(node2);
-    trie6.dump("One node removed");
-    cprintf("\n\n");
 
     EXPECT_EQ(trie6.lookup(0x0123000000000000), ptr(1));
     EXPECT_EQ(trie6.lookup(0x0123456700000000), ptr(2));
@@ -123,8 +116,6 @@
     EXPECT_EQ(trie6.lookup(0x0123456789000000), ptr(4));
 
     trie6.remove(node1);
-    trie6.dump("Two nodes removed");
-    cprintf("\n\n");
 
     EXPECT_EQ(trie6.lookup(0x0123000000000000), ptr(1));
     EXPECT_EQ(trie6.lookup(0x0123456700000000), NULL);