diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,11 +1,15 @@
 # Changelog for commonmark-extensions
 
+## 0.2.3.4
+
+  - Require whitespace after definition list marker (#104).
+    Otherwise we can inadvertently clobber strikeout or subscript.
+
 ## 0.2.3.3
 
   - Fix definition_lists extension (#96). We were not properly consuming
     indentation in definitions, which caused problems when the definitions
     themselves contained lists.
-
 
 ## 0.2.3.2
 
diff --git a/commonmark-extensions.cabal b/commonmark-extensions.cabal
--- a/commonmark-extensions.cabal
+++ b/commonmark-extensions.cabal
@@ -1,5 +1,5 @@
 name:           commonmark-extensions
-version:        0.2.3.3
+version:        0.2.3.4
 synopsis:       Pure Haskell commonmark parser.
 description:
    This library provides some useful extensions to core commonmark
diff --git a/src/Commonmark/Extensions/DefinitionList.hs b/src/Commonmark/Extensions/DefinitionList.hs
--- a/src/Commonmark/Extensions/DefinitionList.hs
+++ b/src/Commonmark/Extensions/DefinitionList.hs
@@ -91,6 +91,7 @@
          gobbleUpToSpaces 3
          pos <- getPosition
          symbol ':' <|> symbol '~'
+         lookAhead whitespace
          try (gobbleUpToSpaces 4 <* notFollowedBy whitespace)
            <|> gobbleSpaces 1
            <|> 1 <$ lookAhead lineEnd