diff --git a/llvm/include/llvm/MC/MCAsmInfo.h b/llvm/include/llvm/MC/MCAsmInfo.h
--- a/llvm/include/llvm/MC/MCAsmInfo.h
+++ b/llvm/include/llvm/MC/MCAsmInfo.h
@@ -18,6 +18,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/MC/MCDirectives.h"
 #include "llvm/MC/MCTargetOptions.h"
+#include <cstdint>
 #include <vector>
 
 namespace llvm {
@@ -855,6 +856,9 @@
   bool hasMipsExpressions() const { return HasMipsExpressions; }
   bool needsFunctionDescriptors() const { return NeedsFunctionDescriptors; }
   bool shouldUseMotorolaIntegers() const { return UseMotorolaIntegers; }
+
+  /// .align 0 may have architecture specific meaning.
+  virtual void handleAlignmentZero(int64_t *Alignment) const;
 };
 
 } // end namespace llvm
diff --git a/llvm/lib/MC/MCAsmInfo.cpp b/llvm/lib/MC/MCAsmInfo.cpp
--- a/llvm/lib/MC/MCAsmInfo.cpp
+++ b/llvm/lib/MC/MCAsmInfo.cpp
@@ -136,3 +136,8 @@
   return SectionName == ".text" || SectionName == ".data" ||
         (SectionName == ".bss" && !usesELFSectionDirectiveForBSS());
 }
+
+void MCAsmInfo::handleAlignmentZero(int64_t *Alignment) const {
+  assert(*Alignment == 0 && "caller should check that alignment is zero");
+  *Alignment = 1;
+}
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -3411,7 +3411,9 @@
   bool ReturnVal = false;
 
   // Compute alignment in bytes.
-  if (IsPow2) {
+  if (Alignment == 0) {
+    Lexer.getMAI().handleAlignmentZero(&Alignment);
+  } else if (IsPow2) {
     // FIXME: Diagnose overflow.
     if (Alignment >= 32) {
       ReturnVal |= Error(AlignmentLoc, "invalid alignment value");
@@ -3420,11 +3422,8 @@
 
     Alignment = 1ULL << Alignment;
   } else {
-    // Reject alignments that aren't either a power of two or zero,
-    // for gas compatibility. Alignment of zero is silently rounded
-    // up to one.
-    if (Alignment == 0)
-      Alignment = 1;
+    // Reject alignments that aren't either a power of two or > 2**32
+    // for gas compatibility.
     if (!isPowerOf2_64(Alignment))
       ReturnVal |= Error(AlignmentLoc, "alignment must be a power of 2");
     if (!isUInt<32>(Alignment))
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.h b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.h
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.h
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.h
@@ -34,6 +34,7 @@
   explicit ARMELFMCAsmInfo(const Triple &TT);
 
   void setUseIntegratedAssembler(bool Value) override;
+  void handleAlignmentZero(int64_t *Alignment) const override;
 };
 
 class ARMCOFFMCAsmInfoMicrosoft : public MCAsmInfoMicrosoft {
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
@@ -83,6 +83,10 @@
   }
 }
 
+void ARMELFMCAsmInfo::handleAlignmentZero(int64_t *Alignment) const {
+  *Alignment = 4;
+}
+
 void ARMCOFFMCAsmInfoMicrosoft::anchor() { }
 
 ARMCOFFMCAsmInfoMicrosoft::ARMCOFFMCAsmInfoMicrosoft() {
diff --git a/llvm/test/MC/ARM/thumb-text-align0.s b/llvm/test/MC/ARM/thumb-text-align0.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/ARM/thumb-text-align0.s
@@ -0,0 +1,21 @@
+@@ Test the default alignment for text sections
+
+@ RUN: llvm-mc %s -triple=thumbv7-linux-gnueabi -filetype=obj \
+@ RUN:   | llvm-readobj -S - | FileCheck %s
+@ RUN: llvm-mc %s -triple=armv7-linux-gnueabi -filetype=obj \
+@ RUN:   | llvm-readobj -S - | FileCheck %s
+.align 0
+mov pc, lr
+
+@ CHECK:      Name: .text (1)
+@ CHECK-NEXT: Type: SHT_PROGBITS (0x1)
+@ CHECK-NEXT: Flags [ (0x6)
+@ CHECK-NEXT:   SHF_ALLOC (0x2)
+@ CHECK-NEXT:   SHF_EXECINSTR (0x4)
+@ CHECK-NEXT: ]
+@ CHECK-NEXT: Address: 0x0
+@ CHECK-NEXT: Offset: 0x34
+@ CHECK-NEXT: Size: 4
+@ CHECK-NEXT: Link: 0
+@ CHECK-NEXT: Info: 0
+@ CHECK-NEXT: AddressAlignment: 4