diff --git a/implementations/javascript/src/codec.js b/implementations/javascript/src/codec.js
index 9b265cd..53c1cb5 100644
--- a/implementations/javascript/src/codec.js
+++ b/implementations/javascript/src/codec.js
@@ -138,6 +138,7 @@ class Decoder {
 
   mapFromArray(vs) {
     return Map().withMutations((m) => {
+      if (vs.length % 2) throw new DecodeError("Missing dictionary value");
       for (let i = 0; i < vs.length; i += 2) {
         m.set(vs[i], vs[i+1]);
       }
diff --git a/implementations/python/preserves/preserves.py b/implementations/python/preserves/preserves.py
index bbab159..43e6d2e 100644
--- a/implementations/python/preserves/preserves.py
+++ b/implementations/python/preserves/preserves.py
@@ -166,7 +166,10 @@ class ImmutableDict(dict):
         try:
             while True:
                 k = next(i)
-                v = next(i)
+                try:
+                    v = next(i)
+                except StopIteration:
+                    raise DecodeError("Missing dictionary value")
                 result_proxy.__setitem__(k, v)
         except StopIteration:
             pass
diff --git a/tests/samples.bin b/tests/samples.bin
index 3fcec96..e476315 100644
Binary files a/tests/samples.bin and b/tests/samples.bin differ
diff --git a/tests/samples.txt b/tests/samples.txt
index f44bc51..bdaee3a 100644
--- a/tests/samples.txt
+++ b/tests/samples.txt
@@ -36,6 +36,7 @@
    dict2a: @"Missing close brace" <ParseShort "{">
    dict3: @"Duplicate key" <ParseError "{ a: 1, a: 2 }">
    dict4: @"Unexpected close brace" <ParseError "}">
+   dict5: @"Missing value" <DecodeError #hex{b3 31 32 33}>
    double1: <Test #hex{033ff0000000000000} 1.0>
    double2: <Test #hex{03fe3cb7b759bf0426} -1.202e300>
    float1: <Test #hex{023f800000} 1.0f>