diff --git a/source/Octopus.Versioning.Tests/Octopus/OctopusVersionTests.cs b/source/Octopus.Versioning.Tests/Octopus/OctopusVersionTests.cs
index d7fec7e..010c575 100644
--- a/source/Octopus.Versioning.Tests/Octopus/OctopusVersionTests.cs
+++ b/source/Octopus.Versioning.Tests/Octopus/OctopusVersionTests.cs
@@ -1081,7 +1081,25 @@ public void TestOriginalStringIsTheSame(string version)
             0,
             0,
             "123ABC.123")]
-        public void TestVersionNumbersAreDelimited(string inputVersion, int major, int minor, int patch, int revision, string release)
+        [TestCase("1.0_prerelease",
+            1,
+            0,
+            0,
+            0,
+            "prerelease")]
+        [TestCase("V1.0",
+            1,
+            0,
+            0,
+            0,
+            "")]
+        [TestCase("v1.0",
+            1,
+            0,
+            0,
+            0,
+            "")]
+        public void TestVersionNumberVariations(string inputVersion, int major, int minor, int patch, int revision, string release)
         {
             var parsedVersion = OctopusVersionParser.Parse(inputVersion);
             Assert.AreEqual(major, parsedVersion.Major);
diff --git a/source/Octopus.Versioning/Octopus/OctopusVersionParser.cs b/source/Octopus.Versioning/Octopus/OctopusVersionParser.cs
index ea51077..83cd361 100644
--- a/source/Octopus.Versioning/Octopus/OctopusVersionParser.cs
+++ b/source/Octopus.Versioning/Octopus/OctopusVersionParser.cs
@@ -30,13 +30,13 @@ public class OctopusVersionParser
             // Versions can start with an optional V
             @$"\s*(?<{Prefix}>v|V)?" +
             // Get the major version number
-            @$"\s*(?<{Major}>\d+\b)\s*" +
+            @$"\s*(?<{Major}>\d+(?=\b|_))\s*" +
             // Get the minor version number, delimited by a period
-            @$"(?:\.\s*(?<{Minor}>\d+\b)\s*)?" +
+            @$"(?:\.\s*(?<{Minor}>\d+(?=\b|_))\s*)?" +
             // Get the patch version number, delimited by a period
-            @$"(?:\.\s*(?<{Patch}>\d+\b)\s*)?" +
+            @$"(?:\.\s*(?<{Patch}>\d+(?=\b|_))\s*)?" +
             // Get the revision version number, delimited by a period
-            @$"(?:\.\s*(?<{Revision}>\d+\b)\s*)?)?" +
+            @$"(?:\.\s*(?<{Revision}>\d+(?=\b|_))\s*)?)?" +
             // Everything after the last digit and before the plus is the prerelease
             @$"(?:[.\-_\\])?(?<{Prerelease}>(?<{PrereleasePrefix}>[A-Za-z0-9]*?)([.\-_\\](?<{PrereleaseCounter}>[A-Za-z0-9.\-_\\]*?)?)?)?" +
             // The metadata is everything after the plus