diff --git a/racket/src/racket/src/read.c b/racket/src/racket/src/read.c
index db22fbc395..c56242f4c6 100644
--- a/racket/src/racket/src/read.c
+++ b/racket/src/racket/src/read.c
@@ -4474,6 +4474,11 @@ static Scheme_Object *read_compact_svector(CPort *port, int l)
   return o;
 }
 
+static int valid_utf8(const char *s, int l)
+{
+  return (scheme_utf8_decode((const unsigned char *)s, 0, l, NULL, 0, -1, NULL, 0, 0) >= 0);
+}
+
   
 static Scheme_Object *read_escape_from_string(char *s, intptr_t len,
                                               Scheme_Object *rel_to,
@@ -4577,6 +4582,8 @@ static Scheme_Object *read_compact(CPort *port, int use_stack)
       l = read_compact_number(port);
       RANGE_CHECK_GETS(l);
       s = read_compact_chars(port, buffer, BLK_BUF_SIZE, l);
+      if (!valid_utf8(s, l))
+        scheme_ill_formed_code(port);
       v = scheme_intern_exact_symbol(s, l);
 
       if (SAME_OBJ(v, port->magic_sym))
@@ -4609,6 +4616,9 @@ static Scheme_Object *read_compact(CPort *port, int use_stack)
 	RANGE_CHECK_GETS(l);
 	s = read_compact_chars(port, buffer, BLK_BUF_SIZE, l);
 
+        if (!valid_utf8(s, l))
+          scheme_ill_formed_code(port);
+
 	if (uninterned)
 	  v = scheme_make_exact_symbol(s, l);
 	else
@@ -4623,6 +4633,8 @@ static Scheme_Object *read_compact(CPort *port, int use_stack)
       l = read_compact_number(port);
       RANGE_CHECK_GETS(l);
       s = read_compact_chars(port, buffer, BLK_BUF_SIZE, l);
+      if (!valid_utf8(s, l))
+        scheme_ill_formed_code(port);
       v = scheme_intern_exact_keyword(s, l);
       break;
     case CPT_BYTE_STRING:
@@ -5037,6 +5049,8 @@ static Scheme_Object *read_compact(CPort *port, int use_stack)
 	l = ch - CPT_SMALL_SYMBOL_START;
 	RANGE_CHECK_GETS(l);
 	s = read_compact_chars(port, buffer, BLK_BUF_SIZE, l);
+        if (!valid_utf8(s, l))
+          scheme_ill_formed_code(port);
 	v = scheme_intern_exact_symbol(s, l);
 
 	if (SAME_OBJ(v, port->magic_sym))
@@ -5301,6 +5315,9 @@ Scheme_Object *scheme_string_to_submodule_path(char *_s, intptr_t len)
     e[l] = 0;
     pos += l;
 
+    if (!valid_utf8(e, l))
+      return scheme_null;
+
     pr = scheme_make_pair(scheme_intern_exact_symbol(e, l), scheme_null);
     if (last)
       SCHEME_CDR(last) = pr;
diff --git a/racket/src/racket/src/symbol.c b/racket/src/racket/src/symbol.c
index f2de0e28de..9068fdd366 100644
--- a/racket/src/racket/src/symbol.c
+++ b/racket/src/racket/src/symbol.c
@@ -611,11 +611,11 @@ const char *scheme_symbol_name_and_size(Scheme_Object *sym, uintptr_t *length, i
     if (ch > 127) {
       /* Decode UTF-8. */
       mzchar buf[2];
-      int ul = 1;
+      int ul = 2;
       while (1) {
-        if (scheme_utf8_decode_offset_prefix((unsigned char *)s, i, i + ul,
-                                             buf, 0, 1,
-                                             NULL, 0, '?') > 0)
+        if (scheme_utf8_decode((unsigned char *)s, i, i + ul,
+                               buf, 0, 1,
+                               NULL, 0, 0) > 0)
           break;
         ul++;
       }