diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -8586,10 +8586,20 @@
 
     const auto *VecTy = SecondType->getAs<VectorType>();
     if (VecTy &&
-        VecTy->getVectorKind() == VectorType::SveFixedLengthDataVector) {
+        (VecTy->getVectorKind() == VectorType::SveFixedLengthDataVector ||
+         VecTy->getVectorKind() == VectorType::GenericVector)) {
       const LangOptions::LaxVectorConversionKind LVCKind =
           getLangOpts().getLaxVectorConversions();
 
+      // If __ARM_FEATURE_SVE_BITS != N do not allow GNU vector lax conversion.
+      // "Whenever __ARM_FEATURE_SVE_BITS==N, GNUT implicitly
+      // converts to VLAT and VLAT implicitly converts to GNUT."
+      // ACLE Spec Version 00bet6, 3.7.3.2. Behavior common to vectors and
+      // predicates.
+      if (VecTy->getVectorKind() == VectorType::GenericVector &&
+          getTypeSize(SecondType) != getLangOpts().ArmSveVectorBits)
+        return false;
+
       // If -flax-vector-conversions=all is specified, the types are
       // certainly compatible.
       if (LVCKind == LangOptions::LaxVectorConversionKind::All)
diff --git a/clang/test/Sema/aarch64-sve-lax-vector-conversions.c b/clang/test/Sema/aarch64-sve-lax-vector-conversions.c
--- a/clang/test/Sema/aarch64-sve-lax-vector-conversions.c
+++ b/clang/test/Sema/aarch64-sve-lax-vector-conversions.c
@@ -7,32 +7,61 @@
 #include <arm_sve.h>
 
 #define N __ARM_FEATURE_SVE_BITS
-#define FIXED_ATTR __attribute__((arm_sve_vector_bits(N)))
+#define SVE_FIXED_ATTR __attribute__((arm_sve_vector_bits(N)))
+#define GNU_FIXED_ATTR __attribute__((vector_size(N / 8)))
 
-typedef svfloat32_t fixed_float32_t FIXED_ATTR;
-typedef svint32_t fixed_int32_t FIXED_ATTR;
+typedef svfloat32_t sve_fixed_float32_t SVE_FIXED_ATTR;
+typedef svint32_t sve_fixed_int32_t SVE_FIXED_ATTR;
+typedef float gnu_fixed_float32_t GNU_FIXED_ATTR;
+typedef int gnu_fixed_int32_t GNU_FIXED_ATTR;
 
-void allowed_with_integer_lax_conversions() {
-  fixed_int32_t fi32;
+void sve_allowed_with_integer_lax_conversions() {
+  sve_fixed_int32_t fi32;
   svint64_t si64;
 
   // The implicit cast here should fail if -flax-vector-conversions=none, but pass if
   // -flax-vector-conversions={integer,all}.
   fi32 = si64;
-  // lax-vector-none-error@-1 {{assigning to 'fixed_int32_t' (vector of 16 'int' values) from incompatible type}}
+  // lax-vector-none-error@-1 {{assigning to 'sve_fixed_int32_t' (vector of 16 'int' values) from incompatible type}}
   si64 = fi32;
   // lax-vector-none-error@-1 {{assigning to 'svint64_t' (aka '__SVInt64_t') from incompatible type}}
 }
 
-void allowed_with_all_lax_conversions() {
-  fixed_float32_t ff32;
+void sve_allowed_with_all_lax_conversions() {
+  sve_fixed_float32_t ff32;
   svfloat64_t sf64;
 
   // The implicit cast here should fail if -flax-vector-conversions={none,integer}, but pass if
   // -flax-vector-conversions=all.
   ff32 = sf64;
-  // lax-vector-none-error@-1 {{assigning to 'fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
-  // lax-vector-integer-error@-2 {{assigning to 'fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
+  // lax-vector-none-error@-1 {{assigning to 'sve_fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
+  // lax-vector-integer-error@-2 {{assigning to 'sve_fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
+  sf64 = ff32;
+  // lax-vector-none-error@-1 {{assigning to 'svfloat64_t' (aka '__SVFloat64_t') from incompatible type}}
+  // lax-vector-integer-error@-2 {{assigning to 'svfloat64_t' (aka '__SVFloat64_t') from incompatible type}}
+}
+
+void gnu_allowed_with_integer_lax_conversions() {
+  gnu_fixed_int32_t fi32;
+  svint64_t si64;
+
+  // The implicit cast here should fail if -flax-vector-conversions=none, but pass if
+  // -flax-vector-conversions={integer,all}.
+  fi32 = si64;
+  // lax-vector-none-error@-1 {{assigning to 'gnu_fixed_int32_t' (vector of 16 'int' values) from incompatible type}}
+  si64 = fi32;
+  // lax-vector-none-error@-1 {{assigning to 'svint64_t' (aka '__SVInt64_t') from incompatible type}}
+}
+
+void gnu_allowed_with_all_lax_conversions() {
+  gnu_fixed_float32_t ff32;
+  svfloat64_t sf64;
+
+  // The implicit cast here should fail if -flax-vector-conversions={none,integer}, but pass if
+  // -flax-vector-conversions=all.
+  ff32 = sf64;
+  // lax-vector-none-error@-1 {{assigning to 'gnu_fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
+  // lax-vector-integer-error@-2 {{assigning to 'gnu_fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
   sf64 = ff32;
   // lax-vector-none-error@-1 {{assigning to 'svfloat64_t' (aka '__SVFloat64_t') from incompatible type}}
   // lax-vector-integer-error@-2 {{assigning to 'svfloat64_t' (aka '__SVFloat64_t') from incompatible type}}
diff --git a/clang/test/Sema/attr-arm-sve-vector-bits.c b/clang/test/Sema/attr-arm-sve-vector-bits.c
--- a/clang/test/Sema/attr-arm-sve-vector-bits.c
+++ b/clang/test/Sema/attr-arm-sve-vector-bits.c
@@ -272,9 +272,6 @@
 // Test the implicit conversion only applies to valid types
 fixed_bool_t to_fixed_bool_t__from_svint32_t(svint32_t x) { return x; } // expected-error-re {{returning 'svint32_t' (aka '__SVInt32_t') from a function with incompatible result type 'fixed_bool_t' (vector of {{[0-9]+}} 'unsigned char' values)}}
 
-svint64_t to_svint64_t__from_gnu_int32_t(gnu_int32_t x) { return x; } // expected-error-re {{returning 'gnu_int32_t' (vector of {{[0-9]+}} 'int32_t' values) from a function with incompatible result type 'svint64_t' (aka '__SVInt64_t')}}
-gnu_int32_t from_svint64_t__to_gnu_int32_t(svint64_t x) { return x; } // expected-error-re {{returning 'svint64_t' (aka '__SVInt64_t') from a function with incompatible result type 'gnu_int32_t' (vector of {{[0-9]+}} 'int32_t' values)}}
-
 // Test implicit conversion between SVE and GNU vector is invalid when
 // __ARM_FEATURE_SVE_BITS != N
 #if defined(__ARM_FEATURE_SVE_BITS) && __ARM_FEATURE_SVE_BITS == 512
diff --git a/clang/test/SemaCXX/aarch64-sve-lax-vector-conversions.cpp b/clang/test/SemaCXX/aarch64-sve-lax-vector-conversions.cpp
--- a/clang/test/SemaCXX/aarch64-sve-lax-vector-conversions.cpp
+++ b/clang/test/SemaCXX/aarch64-sve-lax-vector-conversions.cpp
@@ -7,32 +7,61 @@
 #include <arm_sve.h>
 
 #define N __ARM_FEATURE_SVE_BITS
-#define FIXED_ATTR __attribute__((arm_sve_vector_bits(N)))
+#define SVE_FIXED_ATTR __attribute__((arm_sve_vector_bits(N)))
+#define GNU_FIXED_ATTR __attribute__((vector_size(N / 8)))
 
-typedef svfloat32_t fixed_float32_t FIXED_ATTR;
-typedef svint32_t fixed_int32_t FIXED_ATTR;
+typedef svfloat32_t sve_fixed_float32_t SVE_FIXED_ATTR;
+typedef svint32_t sve_fixed_int32_t SVE_FIXED_ATTR;
+typedef float gnu_fixed_float32_t GNU_FIXED_ATTR;
+typedef int gnu_fixed_int32_t GNU_FIXED_ATTR;
 
-void allowed_with_integer_lax_conversions() {
-  fixed_int32_t fi32;
+void sve_allowed_with_integer_lax_conversions() {
+  sve_fixed_int32_t fi32;
   svint64_t si64;
 
   // The implicit cast here should fail if -flax-vector-conversions=none, but pass if
   // -flax-vector-conversions={integer,all}.
   fi32 = si64;
-  // lax-vector-none-error@-1 {{assigning to 'fixed_int32_t' (vector of 16 'int' values) from incompatible type}}
+  // lax-vector-none-error@-1 {{assigning to 'sve_fixed_int32_t' (vector of 16 'int' values) from incompatible type}}
   si64 = fi32;
   // lax-vector-none-error@-1 {{assigning to 'svint64_t' (aka '__SVInt64_t') from incompatible type}}
 }
 
-void allowed_with_all_lax_conversions() {
-  fixed_float32_t ff32;
+void sve_allowed_with_all_lax_conversions() {
+  sve_fixed_float32_t ff32;
   svfloat64_t sf64;
 
   // The implicit cast here should fail if -flax-vector-conversions={none,integer}, but pass if
   // -flax-vector-conversions=all.
   ff32 = sf64;
-  // lax-vector-none-error@-1 {{assigning to 'fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
-  // lax-vector-integer-error@-2 {{assigning to 'fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
+  // lax-vector-none-error@-1 {{assigning to 'sve_fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
+  // lax-vector-integer-error@-2 {{assigning to 'sve_fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
+  sf64 = ff32;
+  // lax-vector-none-error@-1 {{assigning to 'svfloat64_t' (aka '__SVFloat64_t') from incompatible type}}
+  // lax-vector-integer-error@-2 {{assigning to 'svfloat64_t' (aka '__SVFloat64_t') from incompatible type}}
+}
+
+void gnu_allowed_with_integer_lax_conversions() {
+  gnu_fixed_int32_t fi32;
+  svint64_t si64;
+
+  // The implicit cast here should fail if -flax-vector-conversions=none, but pass if
+  // -flax-vector-conversions={integer,all}.
+  fi32 = si64;
+  // lax-vector-none-error@-1 {{assigning to 'gnu_fixed_int32_t' (vector of 16 'int' values) from incompatible type}}
+  si64 = fi32;
+  // lax-vector-none-error@-1 {{assigning to 'svint64_t' (aka '__SVInt64_t') from incompatible type}}
+}
+
+void gnu_allowed_with_all_lax_conversions() {
+  gnu_fixed_float32_t ff32;
+  svfloat64_t sf64;
+
+  // The implicit cast here should fail if -flax-vector-conversions={none,integer}, but pass if
+  // -flax-vector-conversions=all.
+  ff32 = sf64;
+  // lax-vector-none-error@-1 {{assigning to 'gnu_fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
+  // lax-vector-integer-error@-2 {{assigning to 'gnu_fixed_float32_t' (vector of 16 'float' values) from incompatible type}}
   sf64 = ff32;
   // lax-vector-none-error@-1 {{assigning to 'svfloat64_t' (aka '__SVFloat64_t') from incompatible type}}
   // lax-vector-integer-error@-2 {{assigning to 'svfloat64_t' (aka '__SVFloat64_t') from incompatible type}}