diff --git a/include/xrpl/protocol/STAmount.h b/include/xrpl/protocol/STAmount.h
index 23e4c5e5b5..f1bab1bcbd 100644
--- a/include/xrpl/protocol/STAmount.h
+++ b/include/xrpl/protocol/STAmount.h
@@ -417,7 +417,7 @@ STAmount
 amountFromQuality(std::uint64_t rate);
 
 STAmount
-amountFromString(Asset const& issue, std::string const& amount);
+amountFromString(Asset const& asset, std::string const& amount);
 
 STAmount
 amountFromJson(SField const& name, Json::Value const& v);
diff --git a/include/xrpl/protocol/STNumber.h b/include/xrpl/protocol/STNumber.h
index c0fce572c8..bf22b9d142 100644
--- a/include/xrpl/protocol/STNumber.h
+++ b/include/xrpl/protocol/STNumber.h
@@ -83,6 +83,19 @@ private:
 std::ostream&
 operator<<(std::ostream& out, STNumber const& rhs);
 
+struct NumberParts
+{
+    std::uint64_t mantissa = 0;
+    int exponent = 0;
+    bool negative = false;
+};
+
+NumberParts
+partsFromString(std::string const& number);
+
+STNumber
+numberFromJson(SField const& field, Json::Value const& value);
+
 }  // namespace ripple
 
 #endif
diff --git a/src/libxrpl/protocol/STAmount.cpp b/src/libxrpl/protocol/STAmount.cpp
index 37830830ad..d9538a88d4 100644
--- a/src/libxrpl/protocol/STAmount.cpp
+++ b/src/libxrpl/protocol/STAmount.cpp
@@ -20,15 +20,14 @@
 #include <xrpl/basics/Log.h>
 #include <xrpl/basics/contract.h>
 #include <xrpl/basics/safe_cast.h>
-#include <xrpl/beast/core/LexicalCast.h>
 #include <xrpl/protocol/Protocol.h>
 #include <xrpl/protocol/STAmount.h>
+#include <xrpl/protocol/STNumber.h>
 #include <xrpl/protocol/SystemParameters.h>
 #include <xrpl/protocol/UintTypes.h>
 #include <xrpl/protocol/jss.h>
 #include <boost/algorithm/string.hpp>
 #include <boost/multiprecision/cpp_int.hpp>
-#include <boost/regex.hpp>
 
 #include <iterator>
 #include <memory>
@@ -833,75 +832,16 @@ amountFromQuality(std::uint64_t rate)
 STAmount
 amountFromString(Asset const& asset, std::string const& amount)
 {
-    static boost::regex const reNumber(
-        "^"                       // the beginning of the string
-        "([-+]?)"                 // (optional) + or - character
-        "(0|[1-9][0-9]*)"         // a number (no leading zeroes, unless 0)
-        "(\\.([0-9]+))?"          // (optional) period followed by any number
-        "([eE]([+-]?)([0-9]+))?"  // (optional) E, optional + or -, any number
-        "$",
-        boost::regex_constants::optimize);
-
-    boost::smatch match;
-
-    if (!boost::regex_match(amount, match, reNumber))
-        Throw<std::runtime_error>("Number '" + amount + "' is not valid");
-
-    // Match fields:
-    //   0 = whole input
-    //   1 = sign
-    //   2 = integer portion
-    //   3 = whole fraction (with '.')
-    //   4 = fraction (without '.')
-    //   5 = whole exponent (with 'e')
-    //   6 = exponent sign
-    //   7 = exponent number
-
-    // CHECKME: Why 32? Shouldn't this be 16?
-    if ((match[2].length() + match[4].length()) > 32)
-        Throw<std::runtime_error>("Number '" + amount + "' is overlong");
-
-    bool negative = (match[1].matched && (match[1] == "-"));
-
-    // Can't specify XRP or MPT using fractional representation
-    if ((asset.native() || asset.holds<MPTIssue>()) && match[3].matched)
+    auto const parts = partsFromString(amount);
+    if ((asset.native() || asset.holds<MPTIssue>()) && parts.exponent < 0)
         Throw<std::runtime_error>(
             "XRP and MPT must be specified as integral amount.");
-
-    std::uint64_t mantissa;
-    int exponent;
-
-    if (!match[4].matched)  // integer only
-    {
-        mantissa =
-            beast::lexicalCastThrow<std::uint64_t>(std::string(match[2]));
-        exponent = 0;
-    }
-    else
-    {
-        // integer and fraction
-        mantissa = beast::lexicalCastThrow<std::uint64_t>(match[2] + match[4]);
-        exponent = -(match[4].length());
-    }
-
-    if (match[5].matched)
-    {
-        // we have an exponent
-        if (match[6].matched && (match[6] == "-"))
-            exponent -= beast::lexicalCastThrow<int>(std::string(match[7]));
-        else
-            exponent += beast::lexicalCastThrow<int>(std::string(match[7]));
-    }
-
-    return {asset, mantissa, exponent, negative};
+    return {asset, parts.mantissa, parts.exponent, parts.negative};
 }
 
 STAmount
 amountFromJson(SField const& name, Json::Value const& v)
 {
-    STAmount::mantissa_type mantissa = 0;
-    STAmount::exponent_type exponent = 0;
-    bool negative = false;
     Asset asset;
 
     Json::Value value;
@@ -993,36 +933,38 @@ amountFromJson(SField const& name, Json::Value const& v)
         }
     }
 
+    NumberParts parts;
+
     if (value.isInt())
     {
         if (value.asInt() >= 0)
         {
-            mantissa = value.asInt();
+            parts.mantissa = value.asInt();
         }
         else
         {
-            mantissa = -value.asInt();
-            negative = true;
+            parts.mantissa = -value.asInt();
+            parts.negative = true;
         }
     }
     else if (value.isUInt())
     {
-        mantissa = v.asUInt();
+        parts.mantissa = v.asUInt();
     }
     else if (value.isString())
     {
-        auto const ret = amountFromString(asset, value.asString());
-
-        mantissa = ret.mantissa();
-        exponent = ret.exponent();
-        negative = ret.negative();
+        parts = partsFromString(value.asString());
+        // Can't specify XRP or MPT using fractional representation
+        if ((asset.native() || asset.holds<MPTIssue>()) && parts.exponent < 0)
+            Throw<std::runtime_error>(
+                "XRP and MPT must be specified as integral amount.");
     }
     else
     {
         Throw<std::runtime_error>("invalid amount type");
     }
 
-    return {name, asset, mantissa, exponent, negative};
+    return {name, asset, parts.mantissa, parts.exponent, parts.negative};
 }
 
 bool
diff --git a/src/libxrpl/protocol/STNumber.cpp b/src/libxrpl/protocol/STNumber.cpp
index 74961bfbca..0164bb806f 100644
--- a/src/libxrpl/protocol/STNumber.cpp
+++ b/src/libxrpl/protocol/STNumber.cpp
@@ -19,8 +19,10 @@
 
 #include <xrpl/protocol/STNumber.h>
 
+#include <xrpl/beast/core/LexicalCast.h>
 #include <xrpl/beast/utility/instrumentation.h>
 #include <xrpl/protocol/SField.h>
+#include <boost/regex.hpp>
 
 namespace ripple {
 
@@ -108,4 +110,101 @@ operator<<(std::ostream& out, STNumber const& rhs)
     return out << rhs.getText();
 }
 
+NumberParts
+partsFromString(std::string const& number)
+{
+    static boost::regex const reNumber(
+        "^"                       // the beginning of the string
+        "([-+]?)"                 // (optional) + or - character
+        "(0|[1-9][0-9]*)"         // a number (no leading zeroes, unless 0)
+        "(\\.([0-9]+))?"          // (optional) period followed by any number
+        "([eE]([+-]?)([0-9]+))?"  // (optional) E, optional + or -, any number
+        "$",
+        boost::regex_constants::optimize);
+
+    boost::smatch match;
+
+    if (!boost::regex_match(number, match, reNumber))
+        Throw<std::runtime_error>("'" + number + "' is not a number");
+
+    // Match fields:
+    //   0 = whole input
+    //   1 = sign
+    //   2 = integer portion
+    //   3 = whole fraction (with '.')
+    //   4 = fraction (without '.')
+    //   5 = whole exponent (with 'e')
+    //   6 = exponent sign
+    //   7 = exponent number
+
+    bool negative = (match[1].matched && (match[1] == "-"));
+
+    std::uint64_t mantissa;
+    int exponent;
+
+    if (!match[4].matched)  // integer only
+    {
+        mantissa =
+            beast::lexicalCastThrow<std::uint64_t>(std::string(match[2]));
+        exponent = 0;
+    }
+    else
+    {
+        // integer and fraction
+        mantissa = beast::lexicalCastThrow<std::uint64_t>(match[2] + match[4]);
+        exponent = -(match[4].length());
+    }
+
+    if (match[5].matched)
+    {
+        // we have an exponent
+        if (match[6].matched && (match[6] == "-"))
+            exponent -= beast::lexicalCastThrow<int>(std::string(match[7]));
+        else
+            exponent += beast::lexicalCastThrow<int>(std::string(match[7]));
+    }
+
+    return {mantissa, exponent, negative};
+}
+
+STNumber
+numberFromJson(SField const& field, Json::Value const& value)
+{
+    NumberParts parts;
+
+    if (value.isInt())
+    {
+        if (value.asInt() >= 0)
+        {
+            parts.mantissa = value.asInt();
+        }
+        else
+        {
+            parts.mantissa = -value.asInt();
+            parts.negative = true;
+        }
+    }
+    else if (value.isUInt())
+    {
+        parts.mantissa = value.asUInt();
+    }
+    else if (value.isString())
+    {
+        parts = partsFromString(value.asString());
+        // Only strings can represent out-of-range values.
+        if (parts.mantissa > std::numeric_limits<std::int64_t>::max())
+            Throw<std::range_error>("too high");
+    }
+    else
+    {
+        Throw<std::runtime_error>("not a number");
+    }
+
+    std::int64_t mantissa = parts.mantissa;
+    if (parts.negative)
+        mantissa = -mantissa;
+
+    return STNumber{field, Number{mantissa, parts.exponent}};
+}
+
 }  // namespace ripple
diff --git a/src/libxrpl/protocol/STParsedJSON.cpp b/src/libxrpl/protocol/STParsedJSON.cpp
index 7d08993a8b..6410051bde 100644
--- a/src/libxrpl/protocol/STParsedJSON.cpp
+++ b/src/libxrpl/protocol/STParsedJSON.cpp
@@ -32,6 +32,7 @@
 #include <xrpl/protocol/STBlob.h>
 #include <xrpl/protocol/STInteger.h>
 #include <xrpl/protocol/STIssue.h>
+#include <xrpl/protocol/STNumber.h>
 #include <xrpl/protocol/STParsedJSON.h>
 #include <xrpl/protocol/STPathSet.h>
 #include <xrpl/protocol/STVector256.h>
@@ -574,6 +575,20 @@ parseLeaf(
 
             break;
 
+        case STI_NUMBER:
+            try
+            {
+                ret =
+                    detail::make_stvar<STNumber>(numberFromJson(field, value));
+            }
+            catch (std::exception const&)
+            {
+                error = invalid_data(json_name, fieldName);
+                return ret;
+            }
+
+            break;
+
         case STI_VECTOR256:
             if (!value.isArrayOrNull())
             {
diff --git a/src/libxrpl/protocol/STVar.cpp b/src/libxrpl/protocol/STVar.cpp
index c5d3102bfa..f997604e78 100644
--- a/src/libxrpl/protocol/STVar.cpp
+++ b/src/libxrpl/protocol/STVar.cpp
@@ -188,6 +188,9 @@ STVar::constructST(SerializedTypeID id, int depth, Args&&... args)
         case STI_AMOUNT:
             construct<STAmount>(std::forward<Args>(args)...);
             return;
+        case STI_NUMBER:
+            construct<STNumber>(std::forward<Args>(args)...);
+            return;
         case STI_UINT128:
             construct<STUInt128>(std::forward<Args>(args)...);
             return;
diff --git a/src/test/protocol/STNumber_test.cpp b/src/test/protocol/STNumber_test.cpp
index ed255e32f1..6a3afc5e0a 100644
--- a/src/test/protocol/STNumber_test.cpp
+++ b/src/test/protocol/STNumber_test.cpp
@@ -78,6 +78,15 @@ struct STNumber_test : public beast::unit_test::suite
             STAmount const totalAmount{totalValue, strikePrice.issue()};
             BEAST_EXPECT(totalAmount == Number{10'000});
         }
+
+        {
+            BEAST_EXPECT(
+                numberFromJson(sfNumber, "123") == STNumber(sfNumber, 123));
+            BEAST_EXPECT(
+                numberFromJson(sfNumber, "3.14e2") == STNumber(sfNumber, 314));
+            BEAST_EXPECT(
+                numberFromJson(sfNumber, "1000e-2") == STNumber(sfNumber, 10));
+        }
     }
 };