diff --git a/doc/manual/rl-next/json-number-overflow.md b/doc/manual/rl-next/json-number-overflow.md
new file mode 100644
index 000000000..27850364a
--- /dev/null
+++ b/doc/manual/rl-next/json-number-overflow.md
@@ -0,0 +1,16 @@
+---
+synopsis: Parse overflowing JSON number literals as floating‐point
+issues: []
+cls: [3919]
+category: "Fixes"
+credits: [emilazy]
+---
+
+Previously, `builtins.fromJSON "-9223372036854775809"` would
+return a floating‐point number, while `builtins.fromJSON
+"9223372036854775808"` would cause an evaluation error. This was
+introduced with the banning of integer overflow in Lix 2.91; previously
+the latter would result in C++ undefined behaviour. These cases are
+now treated consistently with JSON’s model of a single numeric type,
+and JSON number literals that do not fit in a Nix‐language integer
+will be parsed as floating‐point numbers.
diff --git a/lix/libexpr/json-to-value.cc b/lix/libexpr/json-to-value.cc
index caddd0366..58c91a0bd 100644
--- a/lix/libexpr/json-to-value.cc
+++ b/lix/libexpr/json-to-value.cc
@@ -108,7 +108,9 @@ public:
     bool number_unsigned(number_unsigned_t val_) override
     {
         if (val_ > std::numeric_limits<NixInt::Inner>::max()) {
-            throw Error("unsigned json number %1% outside of Nix integer range", val_);
+            // Parse as a float for consistency with signed integers
+            // and interoperability with JSON’s single numeric type.
+            return number_float(static_cast<number_float_t>(val_), "");
         }
         NixInt::Inner val = val_;
         rs->value(state).mkInt(val);
diff --git a/tests/functional2/lang/fromJSON-overflowing/eval-fail-overflow.err.exp b/tests/functional2/lang/fromJSON-overflowing/eval-fail-overflow.err.exp
deleted file mode 100644
index 49b8bf8b7..000000000
--- a/tests/functional2/lang/fromJSON-overflowing/eval-fail-overflow.err.exp
+++ /dev/null
@@ -1,8 +0,0 @@
-error:
-       … while calling the 'fromJSON' builtin
-         at /pwd/in.nix:1:1:
-            1| builtins.fromJSON ''{"attr": 18446744073709551615}''
-             | ^
-            2|
-
-       error: unsigned json number 18446744073709551615 outside of Nix integer range
diff --git a/tests/functional2/lang/fromJSON-overflowing/eval-okay-overflow.out.exp b/tests/functional2/lang/fromJSON-overflowing/eval-okay-overflow.out.exp
new file mode 100644
index 000000000..deb1ba3b1
--- /dev/null
+++ b/tests/functional2/lang/fromJSON-overflowing/eval-okay-overflow.out.exp
@@ -0,0 +1 @@
+{ attr = 1.84467e+19; }