diff --git a/lib/nanoc/data_sources/filesystem.rb b/lib/nanoc/data_sources/filesystem.rb
index c697fc8ee2..5fdce86dfc 100644
--- a/lib/nanoc/data_sources/filesystem.rb
+++ b/lib/nanoc/data_sources/filesystem.rb
@@ -117,7 +117,7 @@ def read_proto_document(content_filename, meta_filename, klass)
 
         ProtoDocument.new(is_binary: true, filename: content_filename, attributes: meta)
       elsif is_binary && klass == Nanoc::Int::Layout
-        raise "The layout file '#{content_filename}' is a binary file, but layouts can only be textual"
+        raise Errors::BinaryLayout.new(content_filename)
       else
         parse_result = parse(content_filename, meta_filename)
 
@@ -239,11 +239,11 @@ def all_split_files_in(dir_name)
 
         # Check number of files per type
         unless [0, 1].include?(meta_filenames.size)
-          raise "Found #{meta_filenames.size} meta files for #{basename}; expected 0 or 1"
+          raise Errors::MultipleMetaFiles.new(meta_filenames, basename)
         end
         unless config[:identifier_type] == 'full'
           unless [0, 1].include?(content_filenames.size)
-            raise "Found #{content_filenames.size} content files for #{basename}; expected 0 or 1"
+            raise Errors::MultipleContentFiles.new(meta_filenames, basename)
           end
         end
 
@@ -352,7 +352,7 @@ def parse_with_frontmatter(content_filename)
 
       pieces = data.split(/^(-{5}|-{3})[ \t]*\r?\n?/, 3)
       if pieces.size < 4
-        raise "The file '#{content_filename}' appears to start with a metadata section (three or five dashes at the top) but it does not seem to be in the correct format."
+        raise Errors::InvalidFormat.new(content_filename)
       end
 
       meta = parse_metadata(pieces[2], content_filename)
@@ -366,7 +366,7 @@ def parse_metadata(data, filename)
       begin
         meta = YAML.load(data) || {}
       rescue => e
-        raise "Could not parse YAML for #{filename}: #{e.message}"
+        raise Errors::UnparseableMetadata.new(filename, e)
       end
 
       verify_meta(meta, filename)
@@ -386,16 +386,10 @@ def initialize(content:, attributes:, attributes_data:)
       end
     end
 
-    class InvalidMetadataError < Nanoc::Error
-      def initialize(filename, klass)
-        super("The file #{filename} has invalid metadata (expected key-value pairs, found #{klass} instead)")
-      end
-    end
-
     def verify_meta(meta, filename)
       return if meta.is_a?(Hash)
 
-      raise InvalidMetadataError.new(filename, meta.class)
+      raise Errors::InvalidMetadata.new(filename, meta.class)
     end
 
     # Reads the content of the file with the given name and returns a string
@@ -407,7 +401,7 @@ def read(filename)
       begin
         data = File.read(filename)
       rescue => e
-        raise "Could not read #{filename}: #{e.inspect}"
+        raise Errors::FileUnreadable.new(filename, e)
       end
 
       # Fix
@@ -422,11 +416,11 @@ def read(filename)
         begin
           data.encode!('UTF-8')
         rescue
-          raise_encoding_error(filename, original_encoding)
+          raise Errors::InvalidEncoding.new(filename, original_encoding)
         end
 
         unless data.valid_encoding?
-          raise_encoding_error(filename, original_encoding)
+          raise Errors::InvalidEncoding.new(filename, original_encoding)
         end
       end
 
@@ -435,12 +429,8 @@ def read(filename)
 
       data
     end
-
-    # Raises an invalid encoding error for the given filename and encoding.
-    def raise_encoding_error(filename, encoding)
-      raise "Could not read #{filename} because the file is not valid #{encoding}."
-    end
   end
 end
 
 require_relative 'filesystem/tools'
+require_relative 'filesystem/errors'
diff --git a/lib/nanoc/data_sources/filesystem/errors.rb b/lib/nanoc/data_sources/filesystem/errors.rb
new file mode 100644
index 0000000000..99e3ed6957
--- /dev/null
+++ b/lib/nanoc/data_sources/filesystem/errors.rb
@@ -0,0 +1,55 @@
+class Nanoc::DataSources::Filesystem < Nanoc::DataSource
+  # @api private
+  module Errors
+    class Generic < ::Nanoc::Error
+    end
+
+    class BinaryLayout < Generic
+      def initialize(content_filename)
+        super("The layout file '#{content_filename}' is a binary file, but layouts can only be textual")
+      end
+    end
+
+    class MultipleMetaFiles < Generic
+      def initialize(meta_filenames, basename)
+        super("Found #{meta_filenames.size} meta files for #{basename}; expected 0 or 1")
+      end
+    end
+
+    class MultipleContentFiles < Generic
+      def initialize(content_filenames, basename)
+        super("Found #{content_filenames.size} content files for #{basename}; expected 0 or 1")
+      end
+    end
+
+    class InvalidFormat < Generic
+      def initialize(content_filename)
+        super("The file '#{content_filename}' appears to start with a metadata section (three or five dashes at the top) but it does not seem to be in the correct format.")
+      end
+    end
+
+    class UnparseableMetadata < Generic
+      def initialize(filename, error)
+        super("Could not parse metadata for #{filename}: #{error.message}")
+      end
+    end
+
+    class InvalidMetadata < Generic
+      def initialize(filename, klass)
+        super("The file #{filename} has invalid metadata (expected key-value pairs, found #{klass} instead)")
+      end
+    end
+
+    class InvalidEncoding < Generic
+      def initialize(filename, encoding)
+        super("Could not read #{filename} because the file is not valid #{encoding}.")
+      end
+    end
+
+    class FileUnreadable < Generic
+      def initialize(filename, error)
+        super("Could not read #{filename}: #{error.inspect}")
+      end
+    end
+  end
+end
diff --git a/test/cli/commands/test_create_site.rb b/test/cli/commands/test_create_site.rb
index 255f4ad71a..3d4c3f3235 100644
--- a/test/cli/commands/test_create_site.rb
+++ b/test/cli/commands/test_create_site.rb
@@ -75,7 +75,7 @@ def test_default_encoding
     FileUtils.cd('foo') do
       # Try with encoding = default encoding = utf-8
       File.open('content/index.html', 'w') { |io| io.write('Hello ' + 0xD6.chr + "!\n") }
-      exception = assert_raises(RuntimeError) do
+      exception = assert_raises(Nanoc::DataSources::Filesystem::Errors::InvalidEncoding) do
         Nanoc::Int::SiteLoader.new.new_from_cwd
       end
       assert_equal 'Could not read content/index.html because the file is not valid UTF-8.', exception.message
diff --git a/test/data_sources/test_filesystem.rb b/test/data_sources/test_filesystem.rb
index f55e326355..d1f9077ac9 100644
--- a/test/data_sources/test_filesystem.rb
+++ b/test/data_sources/test_filesystem.rb
@@ -135,7 +135,7 @@ def test_load_binary_layouts
     File.open('foo/stuff.dat', 'w') { |io| io.write('random binary data') }
 
     # Load
-    assert_raises(RuntimeError) do
+    assert_raises(Nanoc::DataSources::Filesystem::Errors::BinaryLayout) do
       data_source.send(:load_objects, 'foo', Nanoc::Int::Layout)
     end
   end
@@ -642,7 +642,7 @@ def test_all_split_files_in_with_multiple_content_files
     end
 
     # Check
-    assert_raises RuntimeError do
+    assert_raises(Nanoc::DataSources::Filesystem::Errors::MultipleContentFiles) do
       data_source.send(:all_split_files_in, '.')
     end
   end
@@ -829,7 +829,7 @@ def test_parse_embedded_invalid_2
     data_source = Nanoc::DataSources::Filesystem.new(nil, nil, nil, nil)
 
     # Parse it
-    assert_raises(RuntimeError) do
+    assert_raises(Nanoc::DataSources::Filesystem::Errors::InvalidFormat) do
       data_source.instance_eval { parse('test.html', nil) }
     end
   end
@@ -981,7 +981,7 @@ def test_parse_internal_bad_metadata
 
     data_source = Nanoc::DataSources::Filesystem.new(nil, nil, nil, nil)
 
-    assert_raises(Nanoc::DataSources::Filesystem::InvalidMetadataError) do
+    assert_raises(Nanoc::DataSources::Filesystem::Errors::InvalidMetadata) do
       data_source.instance_eval { parse('test.html', nil) }
     end
   end
@@ -992,7 +992,7 @@ def test_parse_external_bad_metadata
 
     data_source = Nanoc::DataSources::Filesystem.new(nil, nil, nil, nil)
 
-    assert_raises(Nanoc::DataSources::Filesystem::InvalidMetadataError) do
+    assert_raises(Nanoc::DataSources::Filesystem::Errors::InvalidMetadata) do
       data_source.instance_eval { parse('test.html', 'test.yaml') }
     end
   end