Index: include/regex
===================================================================
--- include/regex
+++ include/regex
@@ -3442,23 +3442,32 @@
 {
     if (__first != __last)
     {
-        _ForwardIterator __temp = _VSTD::next(__first);
-        if (__temp != __last)
+        if (*__first == '\\')
         {
-            if (*__first == '\\')
+            _ForwardIterator __temp = _VSTD::next(__first);
+            if (__temp == __last)
+                __throw_regex_error<regex_constants::error_escape>();
+
+            switch (*__temp)
             {
-                switch (*__temp)
-                {
-                case '^':
-                case '.':
-                case '*':
-                case '[':
-                case '$':
-                case '\\':
-                    __push_char(*__temp);
-                    __first = ++__temp;
+            case '^':
+            case '.':
+            case '*':
+            case '[':
+            case '$':
+            case '\\':
+                __push_char(*__temp);
+                __first = ++__temp;
+                break;
+            case '(':
+            case ')':
+            case '{':
+            case '}':
+                break;
+            default:
+                if (*__temp >= '1' && *__temp <= '9')
                     break;
-                }
+                __throw_regex_error<regex_constants::error_escape>();
             }
         }
     }
@@ -3473,34 +3482,36 @@
 {
     if (__first != __last)
     {
-        _ForwardIterator __temp = _VSTD::next(__first);
-        if (__temp != __last)
+        if (*__first == '\\')
         {
-            if (*__first == '\\')
+            _ForwardIterator __temp = _VSTD::next(__first);
+            if (__temp == __last)
+                __throw_regex_error<regex_constants::error_escape>();
+
+            switch (*__temp)
             {
-                switch (*__temp)
-                {
-                case '^':
-                case '.':
-                case '*':
-                case '[':
-                case '$':
-                case '\\':
-                case '(':
-                case ')':
-                case '|':
-                case '+':
-                case '?':
-                case '{':
-                case '}':
-                    __push_char(*__temp);
-                    __first = ++__temp;
-                    break;
-                default:
-                    if ((__flags_ & 0x1F0) == awk)
-                        __first = __parse_awk_escape(++__first, __last);
+            case '^':
+            case '.':
+            case '*':
+            case '[':
+            case '$':
+            case '\\':
+            case '(':
+            case ')':
+            case '|':
+            case '+':
+            case '?':
+            case '{':
+            case '}':
+                __push_char(*__temp);
+                __first = ++__temp;
+                break;
+            default:
+                if ((__flags_ & 0x1F0) == awk) {
+                    __first = __parse_awk_escape(++__first, __last);
                     break;
                 }
+                __throw_regex_error<regex_constants::error_escape>();
             }
         }
     }
Index: test/std/re/re.regex/re.regex.construct/bad_escape.pass.cpp
===================================================================
--- test/std/re/re.regex/re.regex.construct/bad_escape.pass.cpp
+++ test/std/re/re.regex/re.regex.construct/bad_escape.pass.cpp
@@ -19,11 +19,13 @@
 #include <cassert>
 #include "test_macros.h"
 
-static bool error_escape_thrown(const char *pat)
+static bool error_escape_thrown(const char *pat,
+                                std::regex_constants::syntax_option_type
+                                    syntax = std::regex_constants::ECMAScript)
 {
     bool result = false;
     try {
-        std::regex re(pat);
+        std::regex re(pat, syntax);
     } catch (const std::regex_error &ex) {
         result = (ex.code() == std::regex_constants::error_escape);
     }
@@ -45,4 +47,58 @@
     assert(!error_escape_thrown("[\\cA]"));
     assert(!error_escape_thrown("\\cA"));
 
+    const std::regex_constants::syntax_option_type basic =
+        std::regex_constants::basic;
+
+    assert(error_escape_thrown("\\a", basic));
+    assert(error_escape_thrown("\\n", basic));
+    assert(error_escape_thrown("\\t", basic));
+    assert(error_escape_thrown("\\0", basic));
+    assert(error_escape_thrown("\\/", basic));
+    assert(error_escape_thrown("\\\n", basic));
+    assert(error_escape_thrown("\\", basic));
+
+    assert(!error_escape_thrown("[\\a]", basic));
+    assert(!error_escape_thrown("\\(a\\)", basic));
+    assert(!error_escape_thrown("\\(ab\\)\\1", basic));
+    assert(!error_escape_thrown("a\\{1,2\\}", basic));
+    assert(!error_escape_thrown("\\.", basic));
+    assert(!error_escape_thrown("\\*", basic));
+
+    const std::regex_constants::syntax_option_type extended =
+        std::regex_constants::extended;
+
+    assert(error_escape_thrown("\\a", extended));
+    assert(error_escape_thrown("\\n", extended));
+    assert(error_escape_thrown("\\t", extended));
+    assert(error_escape_thrown("\\0", extended));
+    assert(error_escape_thrown("(ab)\\1", extended));
+    assert(error_escape_thrown("\\/", extended));
+    assert(error_escape_thrown("\\\n", extended));
+    assert(error_escape_thrown("\\", extended));
+
+    assert(!error_escape_thrown("[\\a]", extended));
+    assert(!error_escape_thrown("\\(a\\)", extended));
+    assert(!error_escape_thrown("\\{\\}", extended));
+    assert(!error_escape_thrown("\\.", extended));
+    assert(!error_escape_thrown("\\*", extended));
+
+    const std::regex_constants::syntax_option_type awk =
+        std::regex_constants::awk;
+
+    assert(error_escape_thrown("\\z", awk));
+    assert(error_escape_thrown("[\\z]", awk));
+    assert(error_escape_thrown("\\9", awk));
+    assert(error_escape_thrown("\\\n", awk));
+    assert(error_escape_thrown("\\", awk));
+
+    assert(!error_escape_thrown("\\n", awk));
+    assert(!error_escape_thrown("\\t", awk));
+    assert(!error_escape_thrown("\\/", awk));
+    assert(!error_escape_thrown("\\(a\\)", awk));
+    assert(!error_escape_thrown("\\{\\}", awk));
+    assert(!error_escape_thrown("\\0", awk));
+    assert(!error_escape_thrown("\\1", awk));
+    assert(!error_escape_thrown("\\.", awk));
+    assert(!error_escape_thrown("\\*", awk));
 }