diff --git a/src/Directory.Build.props b/src/Directory.Build.props
index d390d73..0b809f2 100644
--- a/src/Directory.Build.props
+++ b/src/Directory.Build.props
@@ -26,7 +26,10 @@
   <Target Name="StampSourceRevision"
           BeforeTargets="GetAssemblyVersion;GenerateAssemblyInfo"
           Condition="'$(SourceRevisionId)' == ''">
-    <Exec Command="git -C &quot;$(MSBuildThisFileDirectory)&quot; rev-parse --short HEAD"
+    <!-- The trailing "." is load-bearing: $(MSBuildThisFileDirectory) ends in a path
+         separator, and on Windows that trailing backslash escapes the closing quote,
+         mangling the command so git's stderr got stamped as the revision (NEXT-09). -->
+    <Exec Command="git -C &quot;$(MSBuildThisFileDirectory).&quot; rev-parse --short HEAD"
           ConsoleToMSBuild="true"
           StandardOutputImportance="Low"
           ContinueOnError="true"
@@ -34,7 +37,9 @@
       <Output TaskParameter="ConsoleOutput" PropertyName="_StampedGitSha" />
     </Exec>
     <PropertyGroup>
-      <SourceRevisionId Condition="'$(_StampedGitSha)' != ''">$(_StampedGitSha.Trim())</SourceRevisionId>
+      <!-- Accept only something that looks like a git short SHA; Exec's ConsoleOutput
+           mixes in stderr, so any git failure text must never become the revision. -->
+      <SourceRevisionId Condition="$([System.Text.RegularExpressions.Regex]::IsMatch('$(_StampedGitSha.Trim())', '^[0-9a-f]{7,40}$'))">$(_StampedGitSha.Trim())</SourceRevisionId>
     </PropertyGroup>
   </Target>