diff --git a/CHANGELOG.md b/CHANGELOG.md
index e2cd11d9..b000a7bc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -49,6 +49,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   (previously usage of custom non-ascii tags may have led to invalid YAML that can't be parsed).
 - Anchors now work correctly with empty nodes, #301.
 - Fix incorrect parsing of invalid block mapping syntax, #418.
+- Throw an error if block sequence/mapping indent contains a tab, #80.
 
 
 ## [3.14.1] - 2020-12-07
diff --git a/lib/loader.js b/lib/loader.js
index b6dad5b3..39f13f56 100644
--- a/lib/loader.js
+++ b/lib/loader.js
@@ -150,6 +150,10 @@ function State(input, options) {
   this.lineStart  = 0;
   this.lineIndent = 0;
 
+  // position of first leading tab in the current line,
+  // used to make sure there are no tabs in the indentation
+  this.firstTabInLine = -1;
+
   this.documents = [];
 
   /*
@@ -389,6 +393,7 @@ function readLineBreak(state) {
 
   state.line += 1;
   state.lineStart = state.position;
+  state.firstTabInLine = -1;
 }
 
 function skipSeparationSpace(state, allowComments, checkIndent) {
@@ -397,6 +402,9 @@ function skipSeparationSpace(state, allowComments, checkIndent) {
 
   while (ch !== 0) {
     while (is_WHITE_SPACE(ch)) {
+      if (ch === 0x09/* Tab */ && state.firstTabInLine === -1) {
+        state.firstTabInLine = state.position;
+      }
       ch = state.input.charCodeAt(++state.position);
     }
 
@@ -959,6 +967,10 @@ function readBlockSequence(state, nodeIndent) {
       detected  = false,
       ch;
 
+  // there is a leading tab before this token, so it can't be a block sequence/mapping;
+  // it can still be flow sequence/mapping or a scalar
+  if (state.firstTabInLine !== -1) return false;
+
   if (state.anchor !== null) {
     state.anchorMap[state.anchor] = _result;
   }
@@ -966,6 +978,10 @@ function readBlockSequence(state, nodeIndent) {
   ch = state.input.charCodeAt(state.position);
 
   while (ch !== 0) {
+    if (state.firstTabInLine !== -1) {
+      state.position = state.firstTabInLine;
+      throwError(state, 'tab characters must not be used in indentation');
+    }
 
     if (ch !== 0x2D/* - */) {
       break;
@@ -1030,6 +1046,10 @@ function readBlockMapping(state, nodeIndent, flowIndent) {
       detected      = false,
       ch;
 
+  // there is a leading tab before this token, so it can't be a block sequence/mapping;
+  // it can still be flow sequence/mapping or a scalar
+  if (state.firstTabInLine !== -1) return false;
+
   if (state.anchor !== null) {
     state.anchorMap[state.anchor] = _result;
   }
@@ -1037,6 +1057,11 @@ function readBlockMapping(state, nodeIndent, flowIndent) {
   ch = state.input.charCodeAt(state.position);
 
   while (ch !== 0) {
+    if (!atExplicitKey && state.firstTabInLine !== -1) {
+      state.position = state.firstTabInLine;
+      throwError(state, 'tab characters must not be used in indentation');
+    }
+
     following = state.input.charCodeAt(state.position + 1);
     _line = state.line; // Save the current line.
 
diff --git a/lib/snippet.js b/lib/snippet.js
index c3669229..00e2133c 100644
--- a/lib/snippet.js
+++ b/lib/snippet.js
@@ -21,7 +21,7 @@ function getLine(buffer, lineStart, lineEnd, position, maxLineLength) {
   }
 
   return {
-    str: head + buffer.slice(lineStart, lineEnd) + tail,
+    str: head + buffer.slice(lineStart, lineEnd).replace(/\t/g, '→') + tail,
     pos: position - lineStart + head.length // relative position
   };
 }
diff --git a/test/issues/0080.js b/test/issues/0080.js
new file mode 100644
index 00000000..a0bf3361
--- /dev/null
+++ b/test/issues/0080.js
@@ -0,0 +1,73 @@
+'use strict';
+
+
+const assert = require('assert');
+const yaml = require('../../');
+
+
+it('should throw when tabs are used as indentation', function () {
+  assert.throws(() => yaml.load(`
+ \tfoo: 1
+ bar: 2
+`), /end of the stream or a document separator is expected/);
+
+  assert.throws(() => yaml.load(`
+ foo: 1
+ \tbar: 2
+`), /tab characters must not be used/);
+
+  assert.throws(() => yaml.load(`
+ \t- foo
+ - bar
+`), /end of the stream or a document separator is expected/);
+
+  assert.throws(() => yaml.load(`
+ - foo
+ \t- bar
+`), /tab characters must not be used/);
+});
+
+
+it('should allow tabs inside separation spaces', function () {
+  assert.deepStrictEqual(yaml.load(`
+ foo\t \t:\t \t1\t \t
+\t \t \t
+ bar \t : \t 2 \t
+`), { foo: 1, bar: 2 });
+
+  assert.deepStrictEqual(yaml.load(`
+ -\t \tfoo\t \t
+\t \t \t
+ - \t bar \t 
+`), [ 'foo', 'bar' ]);
+
+  assert.deepStrictEqual(yaml.load(`
+\t{\tfoo\t:\t1\t,\tbar\t:\t2\t}\t
+`), { foo: 1, bar: 2 });
+
+  assert.deepStrictEqual(yaml.load(`
+\t[\tfoo\t,\tbar\t]\t
+`), [ 'foo', 'bar' ]);
+
+  assert.deepStrictEqual(yaml.load(`
+foo: # string indent = 1
+ \t \t1
+  \t 2
+ \t \t3
+`), { foo: '1 2 3' });
+});
+
+
+it('should throw when tabs are used as indentation in strings', function () {
+  assert.throws(() => yaml.load(`
+foo:
+  bar: |
+  \tbaz
+`), /tab characters must not be used/);
+
+  assert.deepStrictEqual(yaml.load(`
+foo:
+  bar: |
+   \tbaz
+`), { foo: { bar: '\tbaz\n' } });
+});