diff --git a/include/nlohmann/detail/input/lexer.hpp b/include/nlohmann/detail/input/lexer.hpp
index 4f85f8132..00a964a17 100644
--- a/include/nlohmann/detail/input/lexer.hpp
+++ b/include/nlohmann/detail/input/lexer.hpp
@@ -1587,9 +1587,13 @@ scan_number_done:
     looked up right before the conversion instead of once when the lexer is
     constructed: a locale change in between (by a parser callback, a SAX
     handler, or another thread) must not truncate the value (#5198). The
-    token has been validated before, so if the conversion still stops early,
-    the locale changed between the lookup and the call, and the conversion is
-    repeated with the new decimal point.
+    token has been validated before, so if the conversion stops early and the
+    decimal point changed in the meantime, the locale changed between the
+    lookup and the call, and the conversion is repeated with the new decimal
+    point. If the decimal point did not change, a retry cannot succeed: the
+    locale's decimal point is not a single character (e.g., the two-byte
+    U+066B of ar_EG.UTF-8 or fa_IR.UTF-8) and cannot be substituted in place.
+    The value strtod parsed up to that point is kept, as before this change.
 
     Note that changing the locale in another thread *while* strtod runs is
     undefined behavior of the C library, which this function cannot prevent.
@@ -1597,9 +1601,9 @@ scan_number_done:
     void convert_float_locale_aware()
     {
         const bool has_dot = decimal_point_position != std::string::npos;
+        char decimal_point = get_decimal_point();
         for (;;)
         {
-            const char decimal_point = get_decimal_point();
             const bool substitute = has_dot && decimal_point != '.';
             if (substitute)
             {
@@ -1619,6 +1623,14 @@ scan_number_done:
             {
                 return;
             }
+
+            // retry only if the locale changed; otherwise, this would loop forever
+            const char current_decimal_point = get_decimal_point();
+            if (current_decimal_point == decimal_point)
+            {
+                return;
+            }
+            decimal_point = current_decimal_point;
         }
     }
 
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 4975ac2a0..5b7c4ec19 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -10679,9 +10679,13 @@ scan_number_done:
     looked up right before the conversion instead of once when the lexer is
     constructed: a locale change in between (by a parser callback, a SAX
     handler, or another thread) must not truncate the value (#5198). The
-    token has been validated before, so if the conversion still stops early,
-    the locale changed between the lookup and the call, and the conversion is
-    repeated with the new decimal point.
+    token has been validated before, so if the conversion stops early and the
+    decimal point changed in the meantime, the locale changed between the
+    lookup and the call, and the conversion is repeated with the new decimal
+    point. If the decimal point did not change, a retry cannot succeed: the
+    locale's decimal point is not a single character (e.g., the two-byte
+    U+066B of ar_EG.UTF-8 or fa_IR.UTF-8) and cannot be substituted in place.
+    The value strtod parsed up to that point is kept, as before this change.
 
     Note that changing the locale in another thread *while* strtod runs is
     undefined behavior of the C library, which this function cannot prevent.
@@ -10689,9 +10693,9 @@ scan_number_done:
     void convert_float_locale_aware()
     {
         const bool has_dot = decimal_point_position != std::string::npos;
+        char decimal_point = get_decimal_point();
         for (;;)
         {
-            const char decimal_point = get_decimal_point();
             const bool substitute = has_dot && decimal_point != '.';
             if (substitute)
             {
@@ -10711,6 +10715,14 @@ scan_number_done:
             {
                 return;
             }
+
+            // retry only if the locale changed; otherwise, this would loop forever
+            const char current_decimal_point = get_decimal_point();
+            if (current_decimal_point == decimal_point)
+            {
+                return;
+            }
+            decimal_point = current_decimal_point;
         }
     }
 
diff --git a/tests/src/unit-locale-cpp.cpp b/tests/src/unit-locale-cpp.cpp
index ef52b9ba4..b83e63bde 100644
--- a/tests/src/unit-locale-cpp.cpp
+++ b/tests/src/unit-locale-cpp.cpp
@@ -345,3 +345,43 @@ TEST_CASE("locale changes between lexer construction and number conversion (#519
 
     std::setlocale(LC_NUMERIC, "C");
 }
+
+TEST_CASE("locale with a multi-byte decimal point")
+{
+    // Some locales use a decimal point that is not a single character, e.g.
+    // U+066B ARABIC DECIMAL SEPARATOR (two bytes in UTF-8). It cannot be
+    // substituted in place for '.', so the strtod fallback stops early. The
+    // conversion must still terminate rather than retry forever.
+    const std::array<const char*, 6> names = {{"ar_EG.UTF-8", "ar_SA.UTF-8", "fa_IR.UTF-8", "ps_AF.UTF-8", "ar_EG", "fa_IR"}};
+    bool tested = false;
+    for (const char* name : names)
+    {
+        if (std::setlocale(LC_NUMERIC, name) == nullptr)
+        {
+            continue;
+        }
+        const std::string decimal_point = std::localeconv()->decimal_point;
+        if (decimal_point.size() < 2)
+        {
+            continue;
+        }
+        CAPTURE(name);
+        tested = true;
+
+        // too many significant digits for Clinger's fast path, and an underflow
+        // that std::from_chars rejects: both reach the strtod fallback
+        json j;
+        CHECK_NOTHROW(j = json::parse("[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]"));
+        CHECK(j.is_array());
+        CHECK(json::accept("3.14159265358979323846"));
+
+        // a value the locale-independent paths convert is not affected
+        CHECK(json::parse("12.5") == 12.5);
+    }
+    if (!tested)
+    {
+        MESSAGE("no locale with a multi-byte decimal point is usable");
+    }
+
+    std::setlocale(LC_NUMERIC, "C");
+}