diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 439e47b209b2f..da68148ddccde 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -722,7 +722,8 @@ Crash and bug fixes
   ``[[assume(expr)]]`` attribute was enclosed in parentheses.  (#GH151529)
 - Fixed a crash when parsing ``#embed`` parameters with unmatched closing brackets. (#GH152829)
 - Fixed a crash when compiling ``__real__`` or ``__imag__`` unary operator on scalar value with type promotion. (#GH160583)
-
+- Fixed a crash when parsing malformed #pragma clang loop vectorize_width(4,8,16)
+  by diagnosing invalid comma-separated argument lists. (#GH166325)
 Improvements
 ^^^^^^^^^^^^
 
diff --git a/clang/lib/Parse/ParsePragma.cpp b/clang/lib/Parse/ParsePragma.cpp
index 7c2b9280f0b76..7e8b339f5be49 100644
--- a/clang/lib/Parse/ParsePragma.cpp
+++ b/clang/lib/Parse/ParsePragma.cpp
@@ -1531,7 +1531,7 @@ bool Parser::HandlePragmaLoopHint(LoopHint &Hint) {
         PP.Lex(Tok); // ,
 
         StateInfo = Tok.getIdentifierInfo();
-        IsScalableStr = StateInfo->getName();
+        IsScalableStr = StateInfo ? StateInfo->getName() : "";
 
         if (IsScalableStr != "scalable" && IsScalableStr != "fixed") {
           Diag(Tok.getLocation(),
diff --git a/clang/test/Parser/pragma-loop-vectorize.cpp b/clang/test/Parser/pragma-loop-vectorize.cpp
new file mode 100644
index 0000000000000..94cc77aa37d4c
--- /dev/null
+++ b/clang/test/Parser/pragma-loop-vectorize.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only %s -verify
+
+void sum_vector(unsigned int A[], unsigned int B[], unsigned int sum[]) {
+  #pragma clang loop vectorize_width(4,8,16) vectorize(assume_safety)
+  // expected-error@-1 {{vectorize_width loop hint malformed; use vectorize_width(X, fixed) or vectorize_width(X, scalable) where X is an integer, or vectorize_width('fixed' or 'scalable')}}
+  // expected-warning@-2 {{extra tokens at end of '#pragma clang loop vectorize_width' - ignored}}
+
+  for (int k = 0; k < 64; k++) {
+    sum[k] = A[k] + 3 * B[k];
+  }
+}