diff --git a/src/core/compile.c b/src/core/compile.c
index 40d2c3e4..9f819a83 100644
--- a/src/core/compile.c
+++ b/src/core/compile.c
@@ -961,8 +961,9 @@ JanetFuncDef *janetc_pop_funcdef(JanetCompiler *c) {
             JANET_OUT_OF_MEMORY;
         }
         memcpy(chunks, scope->ua.chunks, sizeof(uint32_t) * numchunks);
+        /* fprintf(stderr, "slot chunks: %d, scope->ua.count: %d, numchunks: %d\n", slotchunks, scope->ua.count, numchunks); */
         /* Register allocator preallocates some registers [240-255, high 16 bits of chunk index 7], we can ignore those. */
-        if (scope->ua.count > 7) chunks[7] &= 0xFFFFU;
+        if (scope->ua.count > 7 && slotchunks > 7) chunks[7] &= 0xFFFFU;
         def->closure_bitset = chunks;
     }
 
diff --git a/src/core/io.c b/src/core/io.c
index 97668887..43996526 100644
--- a/src/core/io.c
+++ b/src/core/io.c
@@ -723,7 +723,7 @@ void janet_dynprintf(const char *name, FILE *dflt_file, const char *format, ...)
     va_start(args, format);
     JanetType xtype;
     Janet x;
-    if (name[0] == '\0') { /* Allow empty string to just use dflt_file directly */
+    if (!name || name[0] == '\0') { /* Allow NULL or empty string to just use dflt_file directly */
         x = janet_wrap_nil();
         xtype = JANET_NIL;
     } else {
diff --git a/src/mainclient/shell.c b/src/mainclient/shell.c
index 010ea2e5..a6fa79ec 100644
--- a/src/mainclient/shell.c
+++ b/src/mainclient/shell.c
@@ -482,7 +482,7 @@ static void savehistory(void) {
     FILE *history_file = fopen(gbl_history_file, "wb");
     for (int i = 0; i < gbl_history_count; i++) {
         if (gbl_history[i][0]) { /* Drop empty strings */
-            janet_dynprintf("", history_file, "%j\n", janet_cstringv(gbl_history[i]));
+            janet_dynprintf(NULL, history_file, "%j\n", janet_cstringv(gbl_history[i]));
         }
     }
     fclose(history_file);
diff --git a/test/suite-corelib.janet b/test/suite-corelib.janet
index 02cdaaba..a3651cd2 100644
--- a/test/suite-corelib.janet
+++ b/test/suite-corelib.janet
@@ -202,5 +202,10 @@
 (assert-no-error "def destructure splice works 2" (do (def (n) [(splice [])]) n))
 (assert-no-error "var destructure splice works" (do (var [a] [;[1]]) a))
 
-(end-suite)
+# Issue #1702 - fuzz case with upvalues
+(each item [1 2 3]
+  # Generate a lot of upvalues (more than 224)
+  (def ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;out-buf @"")
+  (with-dyns [:out out-buf] 1))
 
+(end-suite)