diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 92fc9381a5868..f3a8367ad16e5 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -390,6 +390,9 @@ Improvements to Clang's diagnostics
   that were previously incorrectly accepted in case of other irrelevant
   conditions are now consistently diagnosed, identical to C++ mode.
 
+- Clang now emits a diagnostic in case `vector_size` or `ext_vector_type`
+  attributes are used with a negative size (#GH165463).
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 4e369be0bbb92..fa509536bf021 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3510,6 +3510,8 @@ def err_init_method_bad_return_type : Error<
   "init methods must return an object pointer type, not %0">;
 def err_attribute_invalid_size : Error<
   "vector size not an integral multiple of component size">;
+def err_attribute_vec_negative_size
+    : Error<"vector must have non-negative size">;
 def err_attribute_zero_size : Error<"zero %0 size">;
 def err_attribute_size_too_large : Error<"%0 size too large">;
 def err_typecheck_sve_rvv_ambiguous : Error<
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 280b3c92cce14..682fd258eccf2 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -2358,6 +2358,11 @@ QualType Sema::BuildVectorType(QualType CurType, Expr *SizeExpr,
     return QualType();
   }
 
+  if (VecSize->isNegative()) {
+    Diag(SizeExpr->getExprLoc(), diag::err_attribute_vec_negative_size);
+    return QualType();
+  }
+
   if (CurType->isDependentType())
     return Context.getDependentVectorType(CurType, SizeExpr, AttrLoc,
                                           VectorKind::Generic);
@@ -2427,6 +2432,11 @@ QualType Sema::BuildExtVectorType(QualType T, Expr *ArraySize,
       return QualType();
     }
 
+    if (vecSize->isNegative()) {
+      Diag(ArraySize->getExprLoc(), diag::err_attribute_vec_negative_size);
+      return QualType();
+    }
+
     if (!vecSize->isIntN(32)) {
       Diag(AttrLoc, diag::err_attribute_size_too_large)
           << ArraySize->getSourceRange() << "vector";
diff --git a/clang/test/SemaCXX/vector.cpp b/clang/test/SemaCXX/vector.cpp
index 808bdb679b09c..06195f039cd92 100644
--- a/clang/test/SemaCXX/vector.cpp
+++ b/clang/test/SemaCXX/vector.cpp
@@ -786,3 +786,16 @@ const long long e = *0; // expected-error {{indirection requires pointer operand
 double f = a - e;       // expected-error {{cannot initialize a variable of type 'double' with an rvalue of type '__attribute__((__vector_size__(1 * sizeof(double)))) double' (vector of 1 'double' value)}}
 int h = c - e;          // expected-error {{cannot initialize a variable of type 'int' with an rvalue of type '__attribute__((__vector_size__(1 * sizeof(long)))) long' (vector of 1 'long' value)}}
 }
+
+typedef int v_neg_size __attribute__((vector_size(-8))); // expected-error{{vector must have non-negative size}}
+typedef int v_neg_size_2 __attribute__((vector_size(-1 * 8))); // expected-error{{vector must have non-negative size}}
+typedef int v_ext_neg_size __attribute__((ext_vector_type(-8))); // expected-error{{vector must have non-negative size}}
+typedef int v_ext_neg_size2 __attribute__((ext_vector_type(-1 * 8))); // expected-error{{vector must have non-negative size}}
+
+
+#if __cplusplus >= 201103L
+
+template <int N> using templated_v_size = int  __attribute__((vector_size(N))); // expected-error{{vector must have non-negative size}}
+templated_v_size<-8> templated_v_neg_size; //expected-note{{in instantiation of template type alias 'templated_v_size' requested here}}
+
+#endif