diff --git a/runtime/src/main/java/org/capnproto/PackedInputStream.java b/runtime/src/main/java/org/capnproto/PackedInputStream.java
index c15cfc1..f0f73e9 100644
--- a/runtime/src/main/java/org/capnproto/PackedInputStream.java
+++ b/runtime/src/main/java/org/capnproto/PackedInputStream.java
@@ -33,11 +33,53 @@ public final class PackedInputStream implements ReadableByteChannel {
             //if (outBuf
 
             if (inBuf.remaining() < 10) {
+                if (out >= outEnd) {
+                    return len;
+                }
+
+                if (inBuf.remaining() == 0) {
+                    // refresh buffer...
+                    continue;
+                }
+
+                //# We have at least 1, but not 10, bytes available. We need to read
+                //# slowly, doing a bounds check on each byte.
+
                 // TODO
+            } else {
+
+                tag = inBuf.get();
+                for (int n = 0; n < 8; ++n) {
+                    boolean isNonzero = (tag & (1 << n)) != 0;
+                    // ...
+                }
+
             }
 
-            // TODO
+            if (tag == 0) {
+                if (inBuf.remaining() == 0) {
+                    throw new Error("Should always have non-empty buffer here.");
+                }
 
+                int runLength = inBuf.get() * 8;
+
+                if (runLength > outEnd - out) {
+                    throw new Error("Packed input did not end cleanly on a segment boundary");
+                }
+
+
+            } else if (tag == (byte)0xff) {
+
+                int runLength = inBuf.get() * 8;
+
+
+                if (inBuf.remaining() >= runLength) {
+
+                } else {
+
+                }
+
+            }
 
             if (out == outEnd) {
                 return len;