diff --git a/.gitmodules b/.gitmodules
index eb19f3c..2e5c5fc 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -4,6 +4,6 @@
 [submodule "third-party/JSONTestSuite"]
 	path = third-party/JSONTestSuite
 	url = https://github.com/nst/JSONTestSuite.git
-[submodule "third-party/fast_double_parser"]
-	path = third-party/fast_double_parser
-	url = https://github.com/lemire/fast_double_parser.git
+[submodule "third-party/fast_float"]
+	path = third-party/fast_float
+	url = https://github.com/fastfloat/fast_float
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 04e182b..2be7aaf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,7 @@
 # Changelog
 
+* Switch from ``fast_double_parser`` to ``fast_float``
+
 **1.6.9 (2025-05-12)**
 
 * Remove unused import to fix installation on Termux (by veka0, [#105](https://github.com/Kijewski/pyjson5/pull/105))
diff --git a/MANIFEST.in b/MANIFEST.in
index 494767a..0fbfc40 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -4,10 +4,10 @@ include Makefile
 include pyjson5.cpp
 include pyjson5.pyx
 include pyproject.toml
-include third-party/fast_double_parser/include/fast_double_parser.h
 include requirements*.txt
 recursive-include docs **
 recursive-include scripts **
 recursive-include src **
 recursive-include third-party/json5-tests **
 recursive-include third-party/JSONTestSuite/test_parsing **
+recursive-include third-party/fast_float/include **
diff --git a/src/_decoder.pyx b/src/_decoder.pyx
index 6038863..af0d114 100644
--- a/src/_decoder.pyx
+++ b/src/_decoder.pyx
@@ -243,14 +243,17 @@ cdef object _decode_string(ReaderRef reader, int32_t *c_in_out):
 
 cdef object _decode_double(StackHeapString[char] &buf, Py_ssize_t start):
     cdef double d0
-    cdef const char *end_of_double
+    cdef from_chars_result result
+
+    if has_invalid_exponent(buf.data()):
+        _raise_unclosed('NumericLiteral', start)
 
     d0 = 0.0  # silence warning
-    end_of_double = parse_number(buf.data(), &d0)
-    if end_of_double != NULL and end_of_double[0] == b'\0':
-        return PyFloat_FromDouble(d0)
+    result = from_chars(buf.data(), buf.data() + buf.size(), d0, fmt_json_or_infnan)
+    if <int>(result.ec):
+        _raise_unclosed('NumericLiteral', start)
 
-    _raise_unclosed('NumericLiteral', start)
+    return PyFloat_FromDouble(d0)
 
 
 cdef object _decode_number_leading_zero(ReaderRef reader, StackHeapString[char] &buf,
diff --git a/src/_fast_float_compat.hpp b/src/_fast_float_compat.hpp
new file mode 100644
index 0000000..203a2c6
--- /dev/null
+++ b/src/_fast_float_compat.hpp
@@ -0,0 +1,50 @@
+#pragma once
+#include "../third-party/fast_float/include/fast_float/float_common.h"
+
+/* This header file is a shim to handle 'enum class' in Cython, which doesn't
+ * namespace properly. */
+namespace chars_format {
+    using chars_format = fast_float::chars_format;
+
+    constexpr chars_format fmt_json_or_infnan = fast_float::chars_format::json_or_infnan;
+}
+
+namespace check_floats {
+    /*
+     * Check for invalid exponents on strings which represent floats.
+     * Does not guarantee that the float is valid -- only that *if* it has an
+     * exponent, the exponent is valid.
+     *
+     * Checks in this order:
+     *
+     * - no exponent                OK (false)
+     *
+     * - nothing after exponent     FAIL (true)
+     *
+     * - a sign (+/-) at the end    FAIL (true)
+     *
+     * - anything after exponent    FAIL (true)
+     *   and optional sign
+     *   which is not a digit
+     *
+     * - nothing failed?            OK (false)
+     */
+    bool has_invalid_exponent(const std::string &s) {
+        auto pos = s.find_first_of("e");
+        if (pos == std::string::npos) return false;
+
+        if (++pos >= s.size()) return true;
+
+        if (s[pos] == '+' || s[pos] == '-') {
+            if (++pos >= s.size()) return true;
+        }
+
+        // Now check the exponent part for a dot ('.') or any other non-digit
+        // character
+        for (; pos < s.size(); ++pos) {
+            if (!isdigit(s[pos])) return true;
+        }
+
+        return false;
+    }
+}
diff --git a/src/_imports.pyx b/src/_imports.pyx
index 834600d..ca94ef1 100644
--- a/src/_imports.pyx
+++ b/src/_imports.pyx
@@ -13,6 +13,7 @@ from cpython.object cimport PyObject, PyObject_GetIter
 from cpython.type cimport PyType_Check
 from cpython.unicode cimport PyUnicode_Check, PyUnicode_FromEncodedObject, PyUnicode_Format
 from libcpp cimport bool as boolean
+from libcpp.string cimport string
 
 
 cdef extern from '<cstddef>' namespace 'std' nogil:
@@ -124,9 +125,20 @@ cdef extern from 'src/_decoder_recursive_select.hpp' namespace 'JSON5EncoderCpp'
 
     DrsKind drs_lookup[128]
 
+cdef extern from 'src/_fast_float_compat.hpp' namespace 'chars_format' nogil:
+    cdef cppclass chars_format:
+        pass
+    cdef const chars_format fmt_json_or_infnan
+
+cdef extern from 'src/_fast_float_compat.hpp' namespace 'check_floats' nogil:
+    cdef boolean has_invalid_exponent(string &s)
+
+cdef extern from 'third-party/fast_float/include/fast_float/fast_float.h' namespace 'fast_float' nogil:
+    ctypedef struct from_chars_result:
+        char *ptr
+        int ec
 
-cdef extern from 'third-party/fast_double_parser/include/fast_double_parser.h' namespace 'fast_double_parser' nogil:
-    const char *parse_number(const char *p, double *outDouble)
+    cdef from_chars_result from_chars(char *first, char *last, double &value, chars_format fmt);
 
 
 cdef extern from 'src/dragonbox.cc' namespace 'dragonbox' nogil:
diff --git a/third-party/fast_double_parser b/third-party/fast_double_parser
deleted file mode 160000
index bc93aee..0000000
--- a/third-party/fast_double_parser
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit bc93aee338615e46faac4140dd60eef761ba5b12
diff --git a/third-party/fast_float b/third-party/fast_float
new file mode 160000
index 0000000..c5a3ca3
--- /dev/null
+++ b/third-party/fast_float
@@ -0,0 +1 @@
+Subproject commit c5a3ca37c459050f367a4cb0b23c862c29242d30