diff --git a/docs/source/supported-types.rst b/docs/source/supported-types.rst
index 7d6ead03..63df38d7 100644
--- a/docs/source/supported-types.rst
+++ b/docs/source/supported-types.rst
@@ -696,9 +696,9 @@ Dict subclasses (`collections.OrderedDict`, for example) are also supported for
 encoding only. To decode into a ``dict`` subclass you'll need to implement a
 ``dec_hook`` (see :doc:`extending`).
 
-JSON and TOML only support key types that encode as strings or integers (for
-example `str`, `int`, `enum.Enum`, `datetime.datetime`, `uuid.UUID`, ...).
-MessagePack and YAML support any hashable for the key type.
+JSON and TOML only support key types that encode as strings or numbers (for
+example `str`, `int`, `float`, `enum.Enum`, `datetime.datetime`, `uuid.UUID`,
+...). MessagePack and YAML support any hashable for the key type.
 
 An error is raised during decoding if the keys or values don't match their
 respective types (if specified).
diff --git a/msgspec/_core.c b/msgspec/_core.c
index c275eb95..1f5d5230 100644
--- a/msgspec/_core.c
+++ b/msgspec/_core.c
@@ -10774,7 +10774,7 @@ ms_decode_decimal_from_float(double val, PathNode *path, MsgspecState *mod) {
         /* For finite values, render as the nearest IEEE754 double in string
          * form, then call decimal.Decimal to parse */
         char buf[24];
-        int n = write_f64(val, buf);
+        int n = write_f64(val, buf, false);
         return ms_decode_decimal(buf, n, true, path, mod);
     }
     else {
@@ -11036,7 +11036,7 @@ parse_number_nonfinite(
     PathNode *path,
     bool strict
 ) {
-    ssize_t size = pend - p;
+    size_t size = pend - p;
     double val;
     if (size == 3) {
         if (
@@ -12565,10 +12565,24 @@ static MS_NOINLINE int
 json_encode_float(EncoderState *self, PyObject *obj) {
     char buf[24];
     double x = PyFloat_AS_DOUBLE(obj);
-    int n = write_f64(x, buf);
+    int n = write_f64(x, buf, false);
     return ms_write(self, buf, n);
 }
 
+static MS_NOINLINE int
+json_encode_float_as_str(EncoderState *self, PyObject *obj) {
+    char buf[24];
+    double x = PyFloat_AS_DOUBLE(obj);
+    int size = write_f64(x, buf, true);
+    if (ms_ensure_space(self, size + 2) < 0) return -1;
+    char *p = self->output_buffer_raw + self->output_len;
+    *p++ = '"';
+    memcpy(p, buf, size);
+    *(p + size) = '"';
+    self->output_len += size + 2;
+    return 0;
+}
+
 static MS_INLINE int
 json_encode_cstr(EncoderState *self, const char *str, Py_ssize_t size) {
     if (ms_ensure_space(self, size + 2) < 0) return -1;
@@ -12940,6 +12954,9 @@ json_encode_dict_key(EncoderState *self, PyObject *obj) {
     if (type == &PyLong_Type) {
         return json_encode_long_as_str(self, obj);
     }
+    else if (type == &PyFloat_Type) {
+        return json_encode_float_as_str(self, obj);
+    }
     else if (Py_TYPE(type) == self->mod->EnumMetaType) {
         return json_encode_enum(self, obj, true);
     }
@@ -12967,7 +12984,7 @@ json_encode_dict_key(EncoderState *self, PyObject *obj) {
     else {
         PyErr_SetString(
             PyExc_TypeError,
-            "Only dicts with str-like or int-like keys are supported"
+            "Only dicts with str-like or number-like keys are supported"
         );
         return -1;
     }
@@ -18560,7 +18577,7 @@ to_builtins_dict(ToBuiltinsState *self, PyObject *obj) {
         new_key = to_builtins(self, key, true);
         if (new_key == NULL) goto cleanup;
         if (self->str_keys) {
-            if (PyLong_CheckExact(new_key)) {
+            if (PyLong_CheckExact(new_key) || PyFloat_CheckExact(new_key)) {
                 PyObject *temp = PyObject_Str(new_key);
                 if (temp == NULL) goto cleanup;
                 Py_DECREF(new_key);
@@ -18569,7 +18586,7 @@ to_builtins_dict(ToBuiltinsState *self, PyObject *obj) {
             else if (!PyUnicode_CheckExact(new_key)) {
                 PyErr_SetString(
                     PyExc_TypeError,
-                    "Only dicts with `str` or `int` keys are supported"
+                    "Only dicts with str-like or number-like keys are supported"
                 );
                 goto cleanup;
             }
diff --git a/msgspec/ryu.h b/msgspec/ryu.h
index 6e7f270c..c6a5a7e0 100644
--- a/msgspec/ryu.h
+++ b/msgspec/ryu.h
@@ -919,16 +919,30 @@ write_exponent(int32_t k, char* buf) {
 
 /* Write a double to buf, requires 24 bytes of space */
 static inline int
-write_f64(double f, char* buf) {
+write_f64(double f, char* buf, bool allow_nonfinite) {
     const uint64_t bits = double_to_bits(f);
     const int sign = ((bits >> (DOUBLE_MANTISSA_BITS + DOUBLE_EXPONENT_BITS)) & 1) != 0;
     const uint64_t ieee_mantissa = bits & ((1ull << DOUBLE_MANTISSA_BITS) - 1);
     const uint32_t ieee_exponent = (uint32_t) ((bits >> DOUBLE_MANTISSA_BITS) & ((1u << DOUBLE_EXPONENT_BITS) - 1));
 
     /* Serialize all non-finite numbers as null */
-    if (ieee_exponent == ((1 << DOUBLE_EXPONENT_BITS) - 1)) {
-        memcpy(buf, "null", 4);
-        return 4;
+    if (MS_UNLIKELY(ieee_exponent == ((1 << DOUBLE_EXPONENT_BITS) - 1))) {
+        if (MS_LIKELY(!allow_nonfinite)) {
+            memcpy(buf, "null", 4);
+            return 4;
+        }
+        else {
+            if (ieee_mantissa == 0) {
+                if (sign) {
+                    memcpy(buf, "-inf", 4);
+                    return 4;
+                }
+                memcpy(buf, "inf", 3);
+                return 3;
+            }
+            memcpy(buf, "nan", 3);
+            return 3;
+        }
     }
 
     if (sign) {
diff --git a/tests/test_common.py b/tests/test_common.py
index 3bd7a62d..72e11453 100644
--- a/tests/test_common.py
+++ b/tests/test_common.py
@@ -3608,12 +3608,15 @@ def test_encode_decimal(self, proto):
         s = str(d)
         assert proto.encode(d) == proto.encode(s)
 
-    def test_decode_decimal_str(self, proto):
-        d = decimal.Decimal("1.5")
-        msg = proto.encode(d)
+    @pytest.mark.parametrize(
+        "val", ["1.5", "InF", "-iNf", "iNfInItY", "-InFiNiTy", "NaN"]
+    )
+    def test_decode_decimal_str(self, val, proto):
+        sol = decimal.Decimal(val)
+        msg = proto.encode(sol)
         res = proto.decode(msg, type=decimal.Decimal)
+        assert str(res) == str(sol)
         assert type(res) is decimal.Decimal
-        assert res == d
 
     def test_decode_decimal_str_invalid(self, proto):
         msg = proto.encode("1..5")
diff --git a/tests/test_json.py b/tests/test_json.py
index 634aff18..7ffa0b03 100644
--- a/tests/test_json.py
+++ b/tests/test_json.py
@@ -1800,11 +1800,12 @@ class Test(NamedTuple):
 
 
 class TestDict:
-    def test_encode_dict_raises_non_string_or_int_keys(self):
+    def test_encode_dict_raises_non_string_or_numeric_keys(self):
         with pytest.raises(
-            TypeError, match="Only dicts with str-like or int-like keys are supported"
+            TypeError,
+            match="Only dicts with str-like or number-like keys are supported",
         ):
-            msgspec.json.encode({"a": 1, 2.5: "bad"})
+            msgspec.json.encode({"a": 1, (1, 2): "bad"})
 
     @pytest.mark.parametrize("x", [{}, {"a": 1}, {"a": 1, "b": 2}])
     def test_roundtrip_dict(self, x):
@@ -1896,11 +1897,13 @@ def test_decode_dict_string_cache_ascii_only(self):
         "key",
         [
             1,
+            1.5,
             FruitInt.APPLE,
             uuid.uuid4(),
             datetime.datetime.now(),
             datetime.date.today(),
             datetime.datetime.now().time(),
+            datetime.timedelta(1.5),
             b"test",
             Decimal("1.5"),
         ],
@@ -1973,6 +1976,19 @@ def test_decode_dict_int_literal_key(self):
         with pytest.raises(msgspec.ValidationError, match="Invalid enum value 3"):
             dec.decode(b'{"-1": 10, "3": 20}')
 
+    def test_encode_dict_float_key(self):
+        msg = {
+            1.5: 1,
+            -1.5: 2,
+            0.0: 3,
+            float("-inf"): 4,
+            float("inf"): 5,
+            float("nan"): 6,
+        }
+        sol = msgspec.json.encode({str(k): v for k, v in msg.items()})
+        res = msgspec.json.encode(msg)
+        assert res == sol
+
     def test_decode_dict_float_key(self):
         msg = {"1.5": 1, "inf": 2, "-inf": 3, "0": 4, "-1.5e12": 5, "123": 6}
         buf = msgspec.json.encode(msg)
@@ -1980,6 +1996,13 @@ def test_decode_dict_float_key(self):
         res = msgspec.json.decode(buf, type=Dict[float, int])
         assert res == sol
 
+    def test_decode_dict_int_or_float_key(self):
+        buf = b'{"1.5": "a", "123": "b"}'
+        sol = {1.5: "a", 123: "b"}
+        res = msgspec.json.decode(buf, type=Dict[Union[int, float], str])
+        assert res == sol
+        assert type(list(res.keys())[-1]) is int
+
     def test_encode_dict_str_subclass_key(self):
         class mystr(str):
             pass
diff --git a/tests/test_to_builtins.py b/tests/test_to_builtins.py
index 046395e3..628f2e23 100644
--- a/tests/test_to_builtins.py
+++ b/tests/test_to_builtins.py
@@ -296,17 +296,13 @@ def test_dict_str_keys(self):
         assert to_builtins({FruitInt.BANANA: 1}, str_keys=True) == {"2": 1}
         assert to_builtins({2: 1}, str_keys=True) == {"2": 1}
 
-        with pytest.raises(
-            TypeError, match="Only dicts with `str` or `int` keys are supported"
-        ):
-            to_builtins({(1, 2): 3}, str_keys=True)
-
     def test_dict_sequence_keys(self):
         msg = {frozenset([1, 2]): 1}
         assert to_builtins(msg) == {(1, 2): 1}
 
         with pytest.raises(
-            TypeError, match="Only dicts with `str` or `int` keys are supported"
+            TypeError,
+            match="Only dicts with str-like or number-like keys are supported",
         ):
             to_builtins(msg, str_keys=True)