diff --git a/polly/include/polly/CodeGen/IslAst.h b/polly/include/polly/CodeGen/IslAst.h
--- a/polly/include/polly/CodeGen/IslAst.h
+++ b/polly/include/polly/CodeGen/IslAst.h
@@ -26,6 +26,9 @@
 #include "llvm/IR/PassManager.h"
 #include "isl/ctx.h"
 
+/// Command line switch whether to model read-only accesses.
+extern bool PollyParallel;
+
 namespace polly {
 using llvm::SmallPtrSet;
 
diff --git a/polly/lib/CodeGen/IslAst.cpp b/polly/lib/CodeGen/IslAst.cpp
--- a/polly/lib/CodeGen/IslAst.cpp
+++ b/polly/lib/CodeGen/IslAst.cpp
@@ -59,10 +59,12 @@
 
 using IslAstUserPayload = IslAstInfo::IslAstUserPayload;
 
-static cl::opt<bool>
-    PollyParallel("polly-parallel",
-                  cl::desc("Generate thread parallel code (isl codegen only)"),
-                  cl::init(false), cl::ZeroOrMore, cl::cat(PollyCategory));
+bool PollyParallel;
+static cl::opt<bool, true>
+    XPollyParallel("polly-parallel",
+                   cl::desc("Generate thread parallel code (isl codegen only)"),
+                   cl::ZeroOrMore, cl::cat(PollyCategory),
+                   cl::location(PollyParallel), cl::init(false));
 
 static cl::opt<bool> PrintAccesses("polly-ast-print-accesses",
                                    cl::desc("Print memory access functions"),
diff --git a/polly/lib/Transform/MatmulOptimizer.cpp b/polly/lib/Transform/MatmulOptimizer.cpp
--- a/polly/lib/Transform/MatmulOptimizer.cpp
+++ b/polly/lib/Transform/MatmulOptimizer.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "polly/MatmulOptimizer.h"
+#include "polly/CodeGen/IslAst.h"
 #include "polly/DependenceInfo.h"
 #include "polly/Options.h"
 #include "polly/ScheduleTreeTransform.h"
@@ -1031,7 +1032,10 @@
                                 const llvm::TargetTransformInfo *TTI,
                                 const Dependences *D) {
   MatMulInfoTy MMI;
-  if (isMatrMultPattern(Node, D, MMI)) {
+  // FIXME: Polly's parallel scheduler and the matrix multiplication
+  // pattern match produce invalid code. Disable the matrix pattern
+  // entirely if `-polly-parallel` is used.
+  if (!PollyParallel && isMatrMultPattern(Node, D, MMI)) {
     LLVM_DEBUG(dbgs() << "The matrix multiplication pattern was detected\n");
     return optimizeMatMulPattern(Node, TTI, MMI);
   }