diff --git a/src/core/inttypes.c b/src/core/inttypes.c
index 8ae7b3df..6c90eb0a 100644
--- a/src/core/inttypes.c
+++ b/src/core/inttypes.c
@@ -91,7 +91,8 @@ static const JanetAbstractType it_s64_type = {
     int64_unmarshal,
     it_s64_tostring,
     janet_int64_compare,
-    janet_int64_hash
+    janet_int64_hash,
+    NULL
 };
 
 static const JanetAbstractType it_u64_type = {
@@ -104,7 +105,8 @@ static const JanetAbstractType it_u64_type = {
     int64_unmarshal,
     it_u64_tostring,
     janet_uint64_compare,
-    janet_int64_hash
+    janet_int64_hash,
+    NULL
 };
 
 int64_t janet_unwrap_s64(Janet x) {
diff --git a/src/core/io.c b/src/core/io.c
index 7110491d..ee4e4721 100644
--- a/src/core/io.c
+++ b/src/core/io.c
@@ -52,6 +52,7 @@ JanetAbstractType cfun_io_filetype = {
     NULL,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 
diff --git a/src/core/math.c b/src/core/math.c
index 49b45ec0..d2e507af 100644
--- a/src/core/math.c
+++ b/src/core/math.c
@@ -62,7 +62,8 @@ static JanetAbstractType JanetRNG_type = {
     janet_rng_unmarshal,
     NULL,
     NULL,
-    NULL
+    NULL,
+    NULL,
 };
 
 JanetRNG *janet_default_rng(void) {
diff --git a/src/core/parse.c b/src/core/parse.c
index 90bcb8dc..b4edc2cc 100644
--- a/src/core/parse.c
+++ b/src/core/parse.c
@@ -743,6 +743,7 @@ static JanetAbstractType janet_parse_parsertype = {
     NULL,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 
diff --git a/src/core/peg.c b/src/core/peg.c
index c8298898..41dbafb6 100644
--- a/src/core/peg.c
+++ b/src/core/peg.c
@@ -1214,6 +1214,7 @@ static const JanetAbstractType peg_type = {
     peg_unmarshal,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 
diff --git a/src/core/thread.c b/src/core/thread.c
index 449df4ae..14a4f4e9 100644
--- a/src/core/thread.c
+++ b/src/core/thread.c
@@ -402,6 +402,7 @@ static JanetAbstractType Thread_AT = {
     NULL,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 
diff --git a/src/core/typedarray.c b/src/core/typedarray.c
index ee290607..f4178d73 100644
--- a/src/core/typedarray.c
+++ b/src/core/typedarray.c
@@ -121,6 +121,7 @@ static const JanetAbstractType ta_buffer_type = {
     ta_buffer_unmarshal,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 
@@ -287,6 +288,7 @@ static const JanetAbstractType ta_view_type = {
     ta_view_unmarshal,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 
diff --git a/src/core/util.c b/src/core/util.c
index 919e4e4a..46b38cd9 100644
--- a/src/core/util.c
+++ b/src/core/util.c
@@ -427,6 +427,7 @@ static const JanetAbstractType type_wrap = {
     NULL,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 
diff --git a/src/core/value.c b/src/core/value.c
index a516f811..fff30ac7 100644
--- a/src/core/value.c
+++ b/src/core/value.c
@@ -87,6 +87,12 @@ Janet janet_next(Janet ds, Janet key) {
             }
             break;
         }
+        case JANET_ABSTRACT: {
+            JanetAbstract abst = janet_unwrap_abstract(ds);
+            const JanetAbstractType *at = janet_abstract_type(abst);
+            if (NULL == at->next) break;
+            return at->next(abst, key);
+        }
     }
     return janet_wrap_nil();
 }
diff --git a/src/include/janet.h b/src/include/janet.h
index a7394264..d411bc29 100644
--- a/src/include/janet.h
+++ b/src/include/janet.h
@@ -907,6 +907,7 @@ struct JanetAbstractType {
     void (*tostring)(void *p, JanetBuffer *buffer);
     int (*compare)(void *lhs, void *rhs);
     int32_t (*hash)(void *p, size_t len);
+    Janet(*next)(void *p, Janet key);
 };
 
 struct JanetReg {