diff --git a/src/Humanizer.Tests.Shared/MetricNumeralTests.cs b/src/Humanizer.Tests.Shared/MetricNumeralTests.cs
index 252a753d2..9d719fe14 100644
--- a/src/Humanizer.Tests.Shared/MetricNumeralTests.cs
+++ b/src/Humanizer.Tests.Shared/MetricNumeralTests.cs
@@ -90,24 +90,26 @@ public void TestAllSymbolsAsInt(int exponent)
         }
 
         [Theory]
-        [InlineData("0", 0d, false, true, null)]
-        [InlineData("123", 123d, false, true, null)]
-        [InlineData("-123", (-123d), false, true, null)]
-        [InlineData("1.23k", 1230d, false, true, null)]
-        [InlineData("1 k", 1000d, true, true, null)]
-        [InlineData("1 kilo", 1000d, true, false, null)]
-        [InlineData("1milli", 1E-3, false, false, null)]
-        [InlineData("1.23milli", 1.234E-3, false, false, 2)]
-        [InlineData("12.34k", 12345, false, true, 2)]
-        [InlineData("12k", 12345, false, true, 0)]
-        [InlineData("-3.9m", -3.91e-3, false, true, 1)]
-        public void ToMetric(string expected, double input, bool hasSpace, bool useSymbol, int? decimals)
+        [InlineData("0",         0d,         false, true,  null, null)]
+        [InlineData("123",       123d,       false, true,  null, null)]
+        [InlineData("-123",      (-123d),    false, true,  null, null)]
+        [InlineData("1.23k",     1230d,      false, true,  null, null)]
+        [InlineData("1 k",       1000d,      true,  true,  null, null)]
+        [InlineData("1 kilo",    1000d,      true,  false, null, null)]
+        [InlineData("1milli",    1E-3,       false, false, null, null)]
+        [InlineData("1.23milli", 1.234E-3,   false, false, 2,    null)]
+        [InlineData("12.34k",    12345,      false, true,  2,    null)]
+        [InlineData("12k",       12345,      false, true,  0,    null)]
+        [InlineData("-3.9m",     -3.91e-3,   false, true,  1,    null)]
+        [InlineData("-3.9m",     -3.91e-3,   false, true,  1,    'M')]
+        [InlineData("10M",       10_000_000, false, true,  null, 'G')]
+        [InlineData("10000k",    10_000_000, false, true,  null, 'k')]
+        [InlineData("1234.56k",  1_234_560,  false, true,  null, 'k')]
+        public void ToMetric(string expected, double input, bool hasSpace, bool useSymbol, int? decimals, char? largestPrefix)
         {
-            Assert.Equal(expected, input.ToMetric(hasSpace, useSymbol, decimals));
+            Assert.Equal(expected, input.ToMetric(hasSpace, useSymbol, decimals, largestPrefix));
         }
 
-
-
         [Theory]
         [InlineData(1E+27)]
         [InlineData(1E-27)]
diff --git a/src/Humanizer/MetricNumeralExtensions.cs b/src/Humanizer/MetricNumeralExtensions.cs
index bb1fa37a1..34635dc13 100644
--- a/src/Humanizer/MetricNumeralExtensions.cs
+++ b/src/Humanizer/MetricNumeralExtensions.cs
@@ -243,24 +243,29 @@ private static string BuildRepresentation(double input, bool hasSpace, bool useS
         /// <returns>A number in a Metric representation</returns>
         private static string BuildMetricRepresentation(double input, int exponent, bool hasSpace, bool useSymbol, int? decimals, char? largestPrefix = null)
         {
-            if (largestPrefix != null)
+            if (largestPrefix.HasValue)
                 exponent = LimitExponent(exponent, (char)largestPrefix);
 
             var number = input * Math.Pow(1000, -exponent);
+
             if (decimals.HasValue)
-            {
                 number = Math.Round(number, decimals.Value);
-            }
 
             var symbol = Math.Sign(exponent) == 1
                 ? Symbols[0][exponent - 1]
                 : Symbols[1][-exponent - 1];
+
             return number
                 + (hasSpace ? " " : string.Empty)
                 + GetUnit(symbol, useSymbol);
         }
 
-        // TODO docs
+        /// <summary>
+        /// Limit upper size of exponent value to that corresponding to a metric prefix symbol. TODO synbol or name.
+        /// </summary>
+        /// <param name="exponent">The exponent to limit.</param>
+        /// <param name="useSymbol">True will use symbol instead of name</param>
+        /// <returns>A symbol or a symbol's name</returns>
         private static int LimitExponent(int exponent, char largestPrefix)
         {
             // TODO largestPrefix = largestPrefix.Trim(); When changed to string
@@ -268,9 +273,10 @@ private static int LimitExponent(int exponent, char largestPrefix)
             if (!(Symbols[0].Contains(largestPrefix) || Symbols[1].Contains(largestPrefix)))
                 throw new ArgumentException("Empty or invalid Metric prefix character.", nameof(largestPrefix)); // TODO change to "string".
 
-            return exponent; // TODO
-        }
+            var maxExponent = (Symbols[0].IndexOf(largestPrefix) + 1); // TODO check symbols[1]
 
+            return maxExponent < exponent ? maxExponent : exponent;
+        }
 
         /// <summary>
         /// Get the unit from a symbol of from the symbol's name.