diff --git a/lib/IRGen/IRGenDebugInfo.cpp b/lib/IRGen/IRGenDebugInfo.cpp
index fafb871e3a2..85a4abb5dd6 100644
--- a/lib/IRGen/IRGenDebugInfo.cpp
+++ b/lib/IRGen/IRGenDebugInfo.cpp
@@ -940,6 +940,7 @@ void IRGenDebugInfo::emitVariableDeclaration(
       assert(SizeInBits && "zero-sized piece");
       assert(SizeInBits < VarSizeInBits && "piece covers entire var");
       assert(OffsetInBits+SizeInBits <= VarSizeInBits && "pars > totum");
+      (void) VarSizeInBits;
 
       // Add the piece DWARF expression.
       Operands.push_back(llvm::dwarf::DW_OP_bit_piece);
diff --git a/lib/SILGen/SILGenMaterializeForSet.cpp b/lib/SILGen/SILGenMaterializeForSet.cpp
index a43bdf1bc1c..28394abbfa0 100644
--- a/lib/SILGen/SILGenMaterializeForSet.cpp
+++ b/lib/SILGen/SILGenMaterializeForSet.cpp
@@ -363,6 +363,7 @@ public:
         lv.getSubstFormalType()).getObjectType();
     SILType actualTy = lv.getTypeOfRValue().getObjectType();
     assert(expectedTy == actualTy);
+    (void) expectedTy;
 
     // Reabstract back to the requirement pattern.
     if (actualTy != RequirementStorageType) {
diff --git a/lib/SILOptimizer/IPO/EagerSpecializer.cpp b/lib/SILOptimizer/IPO/EagerSpecializer.cpp
index e3b3e700d20..11bbe0e14ff 100644
--- a/lib/SILOptimizer/IPO/EagerSpecializer.cpp
+++ b/lib/SILOptimizer/IPO/EagerSpecializer.cpp
@@ -273,6 +273,7 @@ void EagerDispatch::emitDispatchTo(SILFunction *NewFunc) {
     ++SubIt;
   }
   assert(SubIt == SubEnd && "Too many substitutions.");
+  (void) SubEnd;
 
   // 2. Convert call arguments, casting and adjusting for calling convention.
 
diff --git a/lib/SILOptimizer/IPO/LetPropertiesOpts.cpp b/lib/SILOptimizer/IPO/LetPropertiesOpts.cpp
index f841ce18b6f..7873d4522ae 100644
--- a/lib/SILOptimizer/IPO/LetPropertiesOpts.cpp
+++ b/lib/SILOptimizer/IPO/LetPropertiesOpts.cpp
@@ -415,6 +415,7 @@ LetPropertiesOpt::analyzeInitValue(SILInstruction *I, VarDecl *Property) {
             (isa<StructElementAddrInst>(Dest) &&
              cast<StructElementAddrInst>(Dest)->getField() == Property)) &&
            "Store instruction should store into a proper let property");
+    (void) Dest;
     ValueOfProperty = SI->getSrc();
   }
 
@@ -491,6 +492,7 @@ void LetPropertiesOpt::collectStructPropertiesAccess(StructInst *SI,
       DEBUG(llvm::dbgs() << "The value of a let property '" << *Prop
                          << "' is not statically known\n");
     }
+    (void) PropValue;
   }
 }
 
diff --git a/lib/Serialization/Deserialization.cpp b/lib/Serialization/Deserialization.cpp
index 4043561e628..e7733de5236 100644
--- a/lib/Serialization/Deserialization.cpp
+++ b/lib/Serialization/Deserialization.cpp
@@ -957,6 +957,7 @@ bool ModuleFile::readDefaultWitnessTable(ProtocolDecl *proto) {
 
   unsigned e = rawWitnessIDs.size();
   assert(e % 2 == 0 && "malformed default witness table");
+  (void) e;
 
   for (unsigned i = 0, e = rawWitnessIDs.size(); i < e; i += 2) {
     ValueDecl *requirement = cast<ValueDecl>(getDecl(rawWitnessIDs[i]));