diff --git a/hydra/grammar/OverrideLexer.g4 b/hydra/grammar/OverrideLexer.g4
index 93dff89326a..82e2670465d 100644
--- a/hydra/grammar/OverrideLexer.g4
+++ b/hydra/grammar/OverrideLexer.g4
@@ -58,7 +58,7 @@ BOOL:
 
 NULL: [Nn][Uu][Ll][Ll];
 
-UNQUOTED_CHAR: [/\-\\+.$%*@];  // other characters allowed in unquoted strings
+UNQUOTED_CHAR: [/\-\\+.$%*@?];  // other characters allowed in unquoted strings
 ID: (CHAR|'_') (CHAR|DIGIT|'_')*;
 // Note: when adding more characters to the ESC rule below, also add them to
 // the `_ESC` string in `_internal/grammar/utils.py`.
diff --git a/hydra/grammar/OverrideParser.g4 b/hydra/grammar/OverrideParser.g4
index 77ef6f97df0..739c257ad74 100644
--- a/hydra/grammar/OverrideParser.g4
+++ b/hydra/grammar/OverrideParser.g4
@@ -59,7 +59,7 @@ primitive:
         | FLOAT                                  // 3.14, -20.0, 1e-1, -10e3
         | BOOL                                   // true, TrUe, false, False
         | INTERPOLATION                          // ${foo.bar}, ${oc.env:USER,me}
-        | UNQUOTED_CHAR                          // /, -, \, +, ., $, %, *, @
+        | UNQUOTED_CHAR                          // /, -, \, +, ., $, %, *, @, ?
         | COLON                                  // :
         | ESC                                    // \\, \(, \), \[, \], \{, \}, \:, \=, \ , \\t, \,
         | WS                                     // whitespaces
@@ -73,7 +73,7 @@ dictKey:
         | INT                                    // 0, 10, -20, 1_000_000
         | FLOAT                                  // 3.14, -20.0, 1e-1, -10e3
         | BOOL                                   // true, TrUe, false, False
-        | UNQUOTED_CHAR                          // /, -, \, +, ., $, %, *, @
+        | UNQUOTED_CHAR                          // /, -, \, +, ., $, %, *, @, ?
         | ESC                                    // \\, \(, \), \[, \], \{, \}, \:, \=, \ , \\t, \,
         | WS                                     // whitespaces
     )+;
diff --git a/news/1597.feature b/news/1597.feature
new file mode 100644
index 00000000000..02a4cb121ea
--- /dev/null
+++ b/news/1597.feature
@@ -0,0 +1 @@
+Override grammar: question marks are now allowed in unquoted strings (e.g. "key=abc?def")
diff --git a/tests/test_overrides_parser.py b/tests/test_overrides_parser.py
index 72c8c75a913..2bdd4a47821 100644
--- a/tests/test_overrides_parser.py
+++ b/tests/test_overrides_parser.py
@@ -31,6 +31,8 @@
 )
 from hydra.errors import HydraException
 
+UNQUOTED_SPECIAL = r"/-\+.$%*@?"  # special characters allowed in unquoted strings
+
 parser = OverridesParser(create_functions())
 
 
@@ -285,7 +287,11 @@ def test_shuffle_sequence(value: str, expected: Any) -> None:
         param("{123: 1, 0: 2, -1: 3}", {123: 1, 0: 2, -1: 3}, id="dict_int_key"),
         param("{3.14: 0, 1e3: 1}", {3.14: 0, 1000.0: 1}, id="dict_float_key"),
         param("{true: 1, fAlSe: 0}", {True: 1, False: 0}, id="dict_bool_key"),
-        param("{/-\\+.$%*@: 1}", {"/-\\+.$%*@": 1}, id="dict_unquoted_char_key"),
+        param(
+            "{%s: 1}" % UNQUOTED_SPECIAL,
+            {UNQUOTED_SPECIAL: 1},
+            id="dict_unquoted_char_key",
+        ),
         param(
             "{\\\\\\(\\)\\[\\]\\{\\}\\:\\=\\ \\\t\\,: 1}",
             {"\\()[]{}:= \t,": 1},
@@ -497,7 +503,7 @@ def test_key(value: str, expected: Any) -> None:
     "value,expected",
     [
         param("a", "a", id="a"),
-        param("/:-\\+.$%*@", "/:-\\+.$%*@", id="accepted_specials"),
+        param(UNQUOTED_SPECIAL, UNQUOTED_SPECIAL, id="accepted_specials"),
         param("abc10", "abc10", id="abc10"),
         param("a.b.c", "a.b.c", id="a.b.c"),
         param("list.0.bar", "list.0.bar", id="list.0.bar"),
@@ -945,8 +951,9 @@ def test_get_key_element(override: str, expected: str) -> None:
             id="dict_quoted_key",
         ),
         param(
-            "key={/-\\+.$%*@: 1}",
-            "{/-\\\\+.$%*@: 1}",  # note that \ gets escaped
+            "key={%s: 1}" % UNQUOTED_SPECIAL,
+            # Note that \ gets escaped.
+            "{%s: 1}" % UNQUOTED_SPECIAL.replace("\\", "\\\\"),
             True,
             id="dict_unquoted_key_special",
         ),
@@ -993,7 +1000,11 @@ def test_override_get_value_element_method(
         param("key={123id: 0}", {"123id": 0}, id="dict_key_int_plus_id"),
         param("key={' abc ': 0}", {" abc ": 0}, id="dict_key_quoted_single"),
         param('key={" abc ": 0}', {" abc ": 0}, id="dict_key_quoted_double"),
-        param("key={a/-\\+.$%*@: 0}", {"a/-\\+.$%*@": 0}, id="dict_key_noquote"),
+        param(
+            "key={a%s: 0}" % UNQUOTED_SPECIAL,
+            {f"a{UNQUOTED_SPECIAL}": 0},
+            id="dict_key_noquote",
+        ),
         param("key={w s: 0}", {"w s": 0}, id="dict_key_ws"),
         param(
             "key={\\\\\\(\\)\\[\\]\\{\\}\\:\\=\\ \\\t\\,: 0}",
diff --git a/website/docs/advanced/override_grammar/basic.md b/website/docs/advanced/override_grammar/basic.md
index 384ef016524..2d037944910 100644
--- a/website/docs/advanced/override_grammar/basic.md
+++ b/website/docs/advanced/override_grammar/basic.md
@@ -85,7 +85,7 @@ primitive:
         | FLOAT                                  // 3.14, -20.0, 1e-1, -10e3
         | BOOL                                   // true, TrUe, false, False
         | INTERPOLATION                          // ${foo.bar}, ${oc.env:USER,me}
-        | UNQUOTED_CHAR                          // /, -, \, +, ., $, %, *, @
+        | UNQUOTED_CHAR                          // /, -, \, +, ., $, %, *, @, ?
         | COLON                                  // :
         | ESC                                    // \\, \(, \), \[, \], \{, \}, \:, \=, \ , \\t, \,
         | WS                                     // whitespaces
@@ -99,7 +99,7 @@ dictKey:
         | INT                                    // 0, 10, -20, 1_000_000
         | FLOAT                                  // 3.14, -20.0, 1e-1, -10e3
         | BOOL                                   // true, TrUe, false, False
-        | UNQUOTED_CHAR                          // /, -, \, +, ., $, %, *, @
+        | UNQUOTED_CHAR                          // /, -, \, +, ., $, %, *, @, ?
         | ESC                                    // \\, \(, \), \[, \], \{, \}, \:, \=, \ , \\t, \,
         | WS                                     // whitespaces
     )+;