diff --git a/io/LasReader.cpp b/io/LasReader.cpp
index 406e78892b..02659d652a 100644
--- a/io/LasReader.cpp
+++ b/io/LasReader.cpp
@@ -159,7 +159,7 @@ void LasReader::initializeLocal(PointTableRef table, MetadataNode& m)
 {
     try
     {
-        m_extraDims = LasUtils::parse(m_extraDimSpec);
+        m_extraDims = LasUtils::parse(m_extraDimSpec, false);
     }
     catch (const LasUtils::error& err)
     {
diff --git a/io/LasUtils.cpp b/io/LasUtils.cpp
index a6515abbae..12d7b8995a 100644
--- a/io/LasUtils.cpp
+++ b/io/LasUtils.cpp
@@ -212,7 +212,7 @@ std::vector<IgnoreVLR> parseIgnoreVLRs(const StringList& ignored)
     return ignoredVLRs;
 
 }
-std::vector<ExtraDim> parse(const StringList& dimString)
+std::vector<ExtraDim> parse(const StringList& dimString, bool allOk)
 {
     std::vector<ExtraDim> extraDims;
     bool all = false;
@@ -221,6 +221,11 @@ std::vector<ExtraDim> parse(const StringList& dimString)
     {
         if (dim == "all")
         {
+            // We only accept all for LasWriter.
+            if (!allOk)
+                throw error("Invalid extra dimension specified: '" + dim +
+                    "'.  Need <dimension>=<type>.  See documentation "
+                    " for details.");
             all = true;
             continue;
         }
diff --git a/io/LasUtils.hpp b/io/LasUtils.hpp
index b87b546127..0c13b33c1b 100644
--- a/io/LasUtils.hpp
+++ b/io/LasUtils.hpp
@@ -171,7 +171,7 @@ struct error : public std::runtime_error
     {}
 };
 
-std::vector<ExtraDim> parse(const StringList& dimString);
+std::vector<ExtraDim> parse(const StringList& dimString, bool allOk);
 
 
 struct IgnoreVLR
diff --git a/io/LasWriter.cpp b/io/LasWriter.cpp
index 4254634a30..bc287d3165 100644
--- a/io/LasWriter.cpp
+++ b/io/LasWriter.cpp
@@ -152,7 +152,7 @@ void LasWriter::initialize()
 #endif
     try
     {
-        m_extraDims = LasUtils::parse(m_extraDimSpec);
+        m_extraDims = LasUtils::parse(m_extraDimSpec, true);
     }
     catch (const LasUtils::error& err)
     {