Index: ELF/ScriptParser.cpp
===================================================================
--- ELF/ScriptParser.cpp
+++ ELF/ScriptParser.cpp
@@ -642,6 +642,17 @@
   }
 }
 
+static Expr checkAlignment(Expr E, std::string &Loc) {
+  return [=] {
+    uint64_t Alignment = std::max((uint64_t)1, E().getValue());
+    if (!isPowerOf2_64(Alignment)) {
+      error(Loc + ": alignment must be power of 2");
+      return (uint64_t)1; // Return a dummy value.
+    }
+    return Alignment;
+  };
+}
+
 OutputSection *ScriptParser::readOutputSectionDescription(StringRef OutSec) {
   OutputSection *Cmd =
       Script->createOutputSection(OutSec, getCurrentLocation());
@@ -650,12 +661,13 @@
     readSectionAddressType(Cmd);
   expect(":");
 
+  std::string Location = getCurrentLocation();
   if (consume("AT"))
     Cmd->LMAExpr = readParenExpr();
   if (consume("ALIGN"))
-    Cmd->AlignExpr = readParenExpr();
+    Cmd->AlignExpr = checkAlignment(readParenExpr(), Location);
   if (consume("SUBALIGN"))
-    Cmd->SubalignExpr = readParenExpr();
+    Cmd->SubalignExpr = checkAlignment(readParenExpr(), Location);
 
   // Parse constraints.
   if (consume("ONLY_IF_RO"))
@@ -959,16 +971,16 @@
   if (Tok == "ALIGN") {
     expect("(");
     Expr E = readExpr();
-    if (consume(")"))
-      return [=] {
-        return alignTo(Script->getDot(), std::max((uint64_t)1, E().getValue()));
-      };
+    if (consume(")")) {
+      E = checkAlignment(E, Location);
+      return [=] { return alignTo(Script->getDot(), E().getValue()); };
+    }
     expect(",");
-    Expr E2 = readExpr();
+    Expr E2 = checkAlignment(readExpr(), Location);
     expect(")");
     return [=] {
       ExprValue V = E();
-      V.Alignment = std::max((uint64_t)1, E2().getValue());
+      V.Alignment = E2().getValue();
       return V;
     };
   }
Index: test/ELF/linkerscript/subalign.s
===================================================================
--- test/ELF/linkerscript/subalign.s
+++ test/ELF/linkerscript/subalign.s
@@ -22,6 +22,23 @@
 # SUBALIGN:   01000000 00000000 02000000 00000000
 # SUBALIGN:   03000000 00000000 04000000 00000000
 
+## Test we do not assert or crash when dot(.) is used inside SUBALIGN. 
+## ld.bfd does not allow to use dot in such expressions, our behavior is inconsistent
+## here for simplicity of implementation. Value of dot is undefined.
+# RUN: echo "SECTIONS { . = 0x32; .aaa : SUBALIGN(.) { *(.aaa*) } }" > %t3.script
+# RUN: ld.lld %t1.o --script %t3.script -o %t3 
+# RUN: llvm-objdump -s %t3 > /dev/null
+
+## Test we are able to link with zero alignment, this is consistent with bfd 2.26.1.
+# RUN: echo "SECTIONS { .aaa : SUBALIGN(0) { *(.aaa*) } }" > %t4.script
+# RUN: ld.lld %t1.o --script %t4.script -o %t4
+# RUN: llvm-objdump -s %t4 | FileCheck -check-prefix=SUBALIGN %s
+
+## Test we fail gracefuly when alignment value is not a power of 2.
+# RUN: echo "SECTIONS { .aaa : SUBALIGN(3) { *(.aaa*) } }" > %t5.script
+# RUN: not ld.lld %t1.o --script %t5.script -o %t5 2>&1 | FileCheck -check-prefix=ERR %s
+# ERR: {{.*}}.script:1: alignment must be power of 2
+
 .global _start
 _start:
  nop