diff --git a/src/de/inetsoftware/jwebassembly/binary/WasmOutputStream.java b/src/de/inetsoftware/jwebassembly/binary/WasmOutputStream.java
index 6d14bc2..6a2ec37 100644
--- a/src/de/inetsoftware/jwebassembly/binary/WasmOutputStream.java
+++ b/src/de/inetsoftware/jwebassembly/binary/WasmOutputStream.java
@@ -69,6 +69,9 @@ class WasmOutputStream extends FilterOutputStream {
      *             if an I/O error occurs.
      */
     void writeVaruint32( @Nonnegative int value ) throws IOException {
+        if( value < 0 ) {
+            throw new IOException( "Invalid negative value" );
+        }
         do {
             int b = value & 0x7F; // low 7 bits
             value >>= 7;