diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -427,7 +427,12 @@
 def ext_pp_opencl_variadic_macros : Extension<
   "variadic macros are a Clang extension in OpenCL">;
 
-def err_pp_invalid_directive : Error<"invalid preprocessing directive">;
+def err_pp_invalid_directive : Error<
+  "invalid preprocessing directive%select{|, did you mean '#%1'?}0"
+>;
+def warn_pp_invalid_directive : Warning<
+  err_pp_invalid_directive.Text>, InGroup<DiagGroup<"unknown-directives">>;
+
 def err_pp_directive_required : Error<
   "%0 must be used within a preprocessing directive">;
 def err_pp_file_not_found : Error<"'%0' file not found">, DefaultFatal;
diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -2241,6 +2241,11 @@
   /// Return true if an error occurs parsing the arg list.
   bool ReadMacroParameterList(MacroInfo *MI, Token& LastTok);
 
+  /// Provide a suggestion for a typoed directive. If there is no typo, then
+  /// just skip suggesting.
+  void SuggestTypoedDirective(const Token &Tok, StringRef Directive,
+                              const SourceLocation &endLoc);
+
   /// We just read a \#if or related directive and decided that the
   /// subsequent tokens are in the \#if'd out portion of the
   /// file.  Lex the rest of the file, until we see an \#endif.  If \p
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -266,6 +266,51 @@
     .Default(false);
 }
 
+/// Find a similar string in `Candidates`.
+///
+/// \param LHS a string for a similar string in `Candidates`
+///
+/// \param Candidates the candidates to find a similar string.
+///
+/// \returns a similar string if exists. If no similar string exists,
+/// returns None.
+static Optional<StringRef> findSimilarStr(
+    StringRef LHS, const std::vector<StringRef> &Candidates) {
+  // We need to check if `Candidates` has the exact case-insensitive string
+  // because the Levenshtein distance match does not care about it.
+  for (StringRef C : Candidates) {
+    if (LHS.equals_insensitive(C)) {
+      return C;
+    }
+  }
+
+  // Keep going with the Levenshtein distance match.
+  // If the LHS size is less than 3, use the LHS size minus 1 and if not,
+  // use the LHS size divided by 3.
+  size_t Length = LHS.size();
+  size_t MaxDist = Length < 3 ? Length - 1 : Length / 3;
+
+  Optional<std::pair<StringRef, size_t>> SimilarStr = None;
+  for (StringRef C : Candidates) {
+    size_t CurDist = LHS.edit_distance(C, true);
+    if (CurDist <= MaxDist) {
+      if (!SimilarStr.hasValue()) {
+        // The first similar string found.
+        SimilarStr = {C, CurDist};
+      } else if (CurDist < SimilarStr->second) {
+        // More similar string found.
+        SimilarStr = {C, CurDist};
+      }
+    }
+  }
+
+  if (SimilarStr.hasValue()) {
+    return SimilarStr->first;
+  } else {
+    return None;
+  }
+}
+
 bool Preprocessor::CheckMacroName(Token &MacroNameTok, MacroUse isDefineUndef,
                                   bool *ShadowFlag) {
   // Missing macro name?
@@ -433,6 +478,27 @@
   return BytesToSkip - LengthDiff;
 }
 
+/// SuggestTypoedDirective - Provide a suggestion for a typoed directive. If
+/// there is no typo, then just skip suggesting.
+void Preprocessor::SuggestTypoedDirective(const Token &Tok, StringRef Directive,
+                                          const SourceLocation &EndLoc) {
+  std::vector<StringRef> Candidates = {
+      "if", "ifdef", "ifndef", "elif", "else", "endif"
+  };
+  if (LangOpts.C2x || LangOpts.CPlusPlus2b) {
+    Candidates.insert(Candidates.end(), {"elifdef", "elifndef"});
+  }
+
+  if (Optional<StringRef> Sugg = findSimilarStr(Directive, Candidates)) {
+    CharSourceRange DirectiveRange =
+        CharSourceRange::getCharRange(Tok.getLocation(), EndLoc);
+    std::string SuggValue = Sugg.getValue().str();
+
+    auto Hint = FixItHint::CreateReplacement(DirectiveRange, "#" + SuggValue);
+    Diag(Tok, diag::warn_pp_invalid_directive) << 1 << SuggValue << Hint;
+  }
+}
+
 /// SkipExcludedConditionalBlock - We just read a \#if or related directive and
 /// decided that the subsequent tokens are in the \#if'd out portion of the
 /// file.  Lex the rest of the file, until we see an \#endif.  If
@@ -556,6 +622,8 @@
         CurPPLexer->pushConditionalLevel(Tok.getLocation(), /*wasskipping*/true,
                                        /*foundnonskip*/false,
                                        /*foundelse*/false);
+      } else {
+        SuggestTypoedDirective(Tok, Directive, endLoc);
       }
     } else if (Directive[0] == 'e') {
       StringRef Sub = Directive.substr(1);
@@ -705,7 +773,11 @@
             break;
           }
         }
+      } else {
+        SuggestTypoedDirective(Tok, Directive, endLoc);
       }
+    } else {
+      SuggestTypoedDirective(Tok, Directive, endLoc);
     }
 
     CurPPLexer->ParsingPreprocessorDirective = false;
@@ -1182,7 +1254,7 @@
   }
 
   // If we reached here, the preprocessing token is not valid!
-  Diag(Result, diag::err_pp_invalid_directive);
+  Diag(Result, diag::err_pp_invalid_directive) << 0;
 
   // Read the rest of the PP line.
   DiscardUntilEndOfDirective();
diff --git a/clang/test/Preprocessor/suggest-typoed-directive.c b/clang/test/Preprocessor/suggest-typoed-directive.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Preprocessor/suggest-typoed-directive.c
@@ -0,0 +1,47 @@
+// RUN: %clang_cc1 -fsyntax-only -verify=not-c2x-cpp2b %s
+// RUN: %clang_cc1 -std=c2x -fsyntax-only -verify=c2x-cpp2b %s
+// RUN: %clang_cc1 -x c++ -std=c++2b -fsyntax-only -verify=c2x-cpp2b %s
+
+// id:        not-c2x-cpp2b-warning@+12 {{invalid preprocessing directive, did you mean '#if'?}}
+// ifd:       not-c2x-cpp2b-warning@+12 {{invalid preprocessing directive, did you mean '#if'?}}
+// ifde:      not-c2x-cpp2b-warning@+12 {{invalid preprocessing directive, did you mean '#ifdef'?}}
+// elf:       not-c2x-cpp2b-warning@+12 {{invalid preprocessing directive, did you mean '#elif'?}}
+// elsif:     not-c2x-cpp2b-warning@+12 {{invalid preprocessing directive, did you mean '#elif'?}}
+// elseif:    not-c2x-cpp2b-warning@+12 {{invalid preprocessing directive, did you mean '#elif'?}}
+// elfidef:   not suggested to '#elifdef'
+// elfindef:  not suggested to '#elifdef'
+// elfinndef: not suggested to '#elifndef'
+// els:       not-c2x-cpp2b-warning@+12 {{invalid preprocessing directive, did you mean '#else'?}}
+// endi:      not-c2x-cpp2b-warning@+12 {{invalid preprocessing directive, did you mean '#endif'?}}
+#ifdef UNDEFINED
+#id
+#ifd
+#ifde
+#elf
+#elsif
+#elseif
+#elfidef
+#elfindef
+#elfinndef
+#els
+#endi
+#endif
+// id:        c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#if'?}}
+// ifd:       c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#if'?}}
+// ifde:      c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#ifdef'?}}
+// elf:       c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#elif'?}}
+// elsif:     c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#elif'?}}
+// elseif:    c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#elif'?}}
+// elfidef:   c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#elifdef'?}}
+// elfindef:  c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#elifdef'?}}
+// elfinndef: c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#elifndef'?}}
+// els:       c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#else'?}}
+// endi:      c2x-cpp2b-warning@-12 {{invalid preprocessing directive, did you mean '#endif'?}}
+
+#ifdef UNDEFINED
+#i // no diagnostic
+#endif
+
+#if special_compiler
+#special_compiler_directive // no diagnostic
+#endif
diff --git a/llvm/include/llvm/ADT/StringRef.h b/llvm/include/llvm/ADT/StringRef.h
--- a/llvm/include/llvm/ADT/StringRef.h
+++ b/llvm/include/llvm/ADT/StringRef.h
@@ -10,6 +10,7 @@
 #define LLVM_ADT_STRINGREF_H
 
 #include "llvm/ADT/DenseMapInfo.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Compiler.h"
@@ -24,6 +25,7 @@
 #endif
 #include <type_traits>
 #include <utility>
+#include <vector>
 
 // Declare the __builtin_strlen intrinsic for MSVC so it can be used in
 // constexpr context.