diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -12052,6 +12052,9 @@
 
   // Strip vector types.
   if (isa<VectorType>(Source)) {
+    // Converting from a vector to a sizeless builtin type is fine.
+    if (Target->isSizelessBuiltinType())
+      return;
     if (!isa<VectorType>(Target)) {
       if (S.SourceMgr.isInSystemMacro(CC))
         return;
diff --git a/clang/test/Sema/aarch64-fixed-vector-to-scalable-implicit-conversion.c b/clang/test/Sema/aarch64-fixed-vector-to-scalable-implicit-conversion.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/aarch64-fixed-vector-to-scalable-implicit-conversion.c
@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve \
+// RUN: -msve-vector-bits=512 -Wconversion -fallow-half-arguments-and-returns \
+// RUN: -o /dev/null %s 2>&1 | FileCheck %s -allow-empty
+
+// CHECK-NOT: warning
+
+#include <arm_sve.h>
+
+#define N __ARM_FEATURE_SVE_BITS
+#define FIXED_ATTR __attribute__((arm_sve_vector_bits(N)))
+
+typedef svbool_t fixed_svbool_t FIXED_ATTR;
+
+fixed_svbool_t check_svnot(fixed_svbool_t p) {
+  return svnot_z(svptrue_b64(), p);
+}
+
+fixed_svbool_t check_svorr(fixed_svbool_t p1, fixed_svbool_t p2) {
+  return svorr_z(svptrue_b64(), p1, p2);
+}
+
+fixed_svbool_t check_svorn(fixed_svbool_t p1, fixed_svbool_t p2) {
+  return svorn_z(svptrue_b64(), p1, p2);
+}
+
+fixed_svbool_t check_svand(fixed_svbool_t p1, fixed_svbool_t p2) {
+  return svand_z(svptrue_b64(), p1, p2);
+}
+
+fixed_svbool_t check_svnand(fixed_svbool_t p1, fixed_svbool_t p2) {
+  return svnand_z(svptrue_b64(), p1, p2);
+}