diff --git a/src/linebuffer.zig b/src/linebuffer.zig
index f48a265..c68d5b6 100644
--- a/src/linebuffer.zig
+++ b/src/linebuffer.zig
@@ -60,6 +60,10 @@ pub fn LineBuffer(comptime options: Strictness) type {
             };
         }
 
+        pub fn empty(self: @This()) bool {
+            return self.internal.empty();
+        }
+
         pub fn deinit(self: @This()) void {
             self.allocator.free(self.internal.buffer);
         }
@@ -112,6 +116,12 @@ pub fn FixedLineBuffer(comptime options: Strictness) type {
             return .{ .buffer = data, .window = .{ .start = 0, .len = data.len } };
         }
 
+        pub fn empty(self: @This()) bool {
+            // we can't check the overall buffer size because the dynamic buffer may be
+            // overallocated
+            return self.window.len == 0;
+        }
+
         pub fn nextLine(self: *@This()) !?[]const u8 {
             if (self.window.start >= self.buffer.len or self.window.len == 0)
                 return null;
diff --git a/src/parser.zig b/src/parser.zig
index f7e0a1e..457c45d 100644
--- a/src/parser.zig
+++ b/src/parser.zig
@@ -54,6 +54,10 @@ pub fn parseBuffer(allocator: std.mem.Allocator, buffer: []const u8, options: Op
     };
 
     while (try tok.next()) |line| try state.parseLine(line, options.duplicate_key_behavior);
+    // state doesn't have access to the tokenizer, which is the only thing that can
+    // error if unparsed lines remain in the buffer by the time that "finish" is
+    // called.
+    try tok.finish();
     return try state.finish(options);
 }
 
@@ -90,6 +94,7 @@ pub const StreamParser = struct {
     }
 
     pub fn finish(self: *StreamParser) !Document {
+        try self.linetok.finish();
         return try self.parse_state.finish(self.parse_options);
     }
 };
diff --git a/src/tokenizer.zig b/src/tokenizer.zig
index e52ba4a..14788e2 100644
--- a/src/tokenizer.zig
+++ b/src/tokenizer.zig
@@ -70,6 +70,12 @@ pub fn LineTokenizer(comptime Buffer: type) type {
         diagnostics: *Diagnostics,
         row: usize = 0,
 
+        pub fn finish(self: @This()) !void {
+            if (!self.buffer.empty()) {
+                return error.ExtraContent;
+            }
+        }
+
         pub fn next(self: *@This()) !?Line {
             lineloop: while (try self.buffer.nextLine()) |raw_line| {
                 var indent: usize = 0;