diff --git a/src/Text/Pandoc/Readers/LaTeX.hs b/src/Text/Pandoc/Readers/LaTeX.hs
index a517f9566..4d50ec4ed 100644
--- a/src/Text/Pandoc/Readers/LaTeX.hs
+++ b/src/Text/Pandoc/Readers/LaTeX.hs
@@ -239,17 +239,28 @@ block = (mempty <$ comment)
 blocks :: LP Blocks
 blocks = mconcat <$> many block
 
+getRawCommand :: String -> LP String
+getRawCommand name' = do
+  rawargs <- withRaw (skipopts *> option "" dimenarg *> many braced)
+  return $ '\\' : name' ++ snd rawargs
+
 blockCommand :: LP Blocks
 blockCommand = try $ do
   name <- anyControlSeq
   guard $ name /= "begin" && name /= "end"
   star <- option "" (string "*" <* optional sp)
   let name' = name ++ star
+  let raw = do
+        rawcommand <- getRawCommand name'
+        transformed <- applyMacros' rawcommand
+        if transformed /= rawcommand
+           then parseFromString blocks transformed
+           else mzero
   case M.lookup name' blockCommands of
        Just p      -> p
        Nothing     -> case M.lookup name blockCommands of
                            Just p    -> p
-                           Nothing   -> mzero
+                           Nothing   -> raw
 
 inBrackets :: Inlines -> Inlines
 inBrackets x = (str "[") <> x <> (str "]")
@@ -385,8 +396,7 @@ inlineCommand = try $ do
   star <- option "" (string "*")
   let name' = name ++ star
   let raw = do
-        rawargs <- withRaw (skipopts *> option "" dimenarg *> many braced)
-        let rawcommand = '\\' : name ++ star ++ snd rawargs
+        rawcommand <- getRawCommand name'
         transformed <- applyMacros' rawcommand
         if transformed /= rawcommand
            then parseFromString inlines transformed
diff --git a/tests/latex-reader.latex b/tests/latex-reader.latex
index 2ebdfed99..0e5983d6a 100644
--- a/tests/latex-reader.latex
+++ b/tests/latex-reader.latex
@@ -845,4 +845,23 @@ indented.
 
 \$ \% \& \# \_ \{ \}
 
+\section{Block newcommands}
+
+See e.g. issues #1866, #1835
+
+\newcommand{\FIG}[3]{
+        \begin{figure}[h!]
+                \centering
+                \includegraphics[width=#2\columnwidth,angle=0]{#1}
+                \caption{#3}
+                \label{fig:#1}
+        \end{figure}
+}
+
+\newcommand{\separator}{\vspace{4em}}
+
+\separator
+
+\FIG{lalune.jpg}{0.5}{Test caption}
+
 \end{document}
diff --git a/tests/latex-reader.native b/tests/latex-reader.native
index abc4b05a7..2cc6508de 100644
--- a/tests/latex-reader.native
+++ b/tests/latex-reader.native
@@ -372,4 +372,8 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
  [[Para [Str "And",Space,Str "in",Space,Str "list",Space,Str "items.",Note [Para [Str "In",Space,Str "list."]]]]]
 ,Para [Str "This",Space,Str "paragraph",Space,Str "should",Space,Str "not",Space,Str "be",Space,Str "part",Space,Str "of",Space,Str "the",Space,Str "note,",Space,Str "as",Space,Str "it",Space,Str "is",Space,Str "not",Space,Str "indented."]
 ,Header 1 ("escaped-characters",[],[]) [Str "Escaped",Space,Str "characters"]
-,Para [Str "$",Space,Str "%",Space,Str "&",Space,Str "#",Space,Str "_",Space,Str "{",Space,Str "}"]]
+,Para [Str "$",Space,Str "%",Space,Str "&",Space,Str "#",Space,Str "_",Space,Str "{",Space,Str "}"]
+,Header 1 ("block-newcommands",[],[]) [Str "Block",Space,Str "newcommands"]
+,Para [Str "See",Space,Str "e.g.",Space,Str "issues",Space,Str "#1866,",Space,Str "#1835"]
+,RawBlock (Format "latex") "\\vspace{4em}"
+,Para [RawInline (Format "latex") "\\centering",Image [Str "Test",Space,Str "caption",Span ("",[],[("data-label","fig:lalune.jpg")]) []] ("lalune.jpg","fig:")]]