Index: lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
+++ lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
@@ -1531,7 +1531,33 @@
 
         CallInst *CustomCI = IRB.CreateCall(CustomF, Args);
         CustomCI->setCallingConv(CI->getCallingConv());
-        CustomCI->setAttributes(CI->getAttributes());
+
+        if (FT->isVarArg()) {
+          AttributeList OldAttrs = CI->getAttributes();
+          SmallVector<AttributeSet, 8> ArgAttrs;
+          const unsigned NonVarArgCount = FT->getNumParams();
+          const unsigned ShadowArgCount =
+              CustomFT->getNumParams() - NonVarArgCount;
+
+          // Copy non-vararg attributes.
+          for (unsigned n = 0; n < NonVarArgCount; n++) {
+            ArgAttrs.push_back(OldAttrs.getParamAttributes(n));
+          }
+          // Skip label parameters.
+          for (unsigned n = 0; n < ShadowArgCount; n++) {
+            ArgAttrs.push_back(AttributeSet());
+          }
+          // Copy vararg attributes.
+          for (unsigned n = NonVarArgCount; n < CS.arg_size(); n++) {
+            ArgAttrs.push_back(OldAttrs.getParamAttributes(n));
+          }
+
+          CustomCI->setAttributes(AttributeList::get(
+              F->getContext(), OldAttrs.getFnAttributes(),
+              OldAttrs.getRetAttributes(), ArgAttrs));
+        } else {
+          CustomCI->setAttributes(CI->getAttributes());
+        }
 
         // Update the parameter attributes of the custom call instruction to
         // zero extend the shadow parameters. This is required for targets
Index: test/Instrumentation/DataFlowSanitizer/Inputs/custom-abilist.txt
===================================================================
--- test/Instrumentation/DataFlowSanitizer/Inputs/custom-abilist.txt
+++ test/Instrumentation/DataFlowSanitizer/Inputs/custom-abilist.txt
@@ -0,0 +1,2 @@
+fun:sprintf=custom
+fun:sprintf=uninstrumented
Index: test/Instrumentation/DataFlowSanitizer/custom-attrs.ll
===================================================================
--- test/Instrumentation/DataFlowSanitizer/custom-attrs.ll
+++ test/Instrumentation/DataFlowSanitizer/custom-attrs.ll
@@ -0,0 +1,16 @@
+; RUN: opt < %s -dfsan -dfsan-args-abi -dfsan-abilist=%S/Inputs/custom-abilist.txt -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f() {
+  ; CHECK: call signext i32 {{.*}} @__dfsw_sprintf(i8* align 1 undef, i8* align 2 undef, i16 zeroext 0, i16 zeroext 0, i16* %{{.*}}, i16* %{{.*}}) #[[ATTR:[0-9]+]]
+  ; CHECK: call signext i32 {{.*}} @__dfsw_sprintf(i8* align 1 undef, i8* align 2 undef, i16 zeroext 0, i16 zeroext 0, i16* %{{.*}}, i16* %{{.*}}, i8* align 4 undef, i8* align 8 undef) #[[ATTR]]
+  ; attributes #[[ATTR]] = { nounwind }
+  call signext i32 (i8*, i8*, ...) @sprintf(i8* align 1 undef, i8* align 2 undef) #1
+  call signext i32 (i8*, i8*, ...) @sprintf(i8* align 1 undef, i8* align 2 undef, i8* align 4 undef, i8* align 8 undef) #1
+  ret void
+}
+
+declare i32 @sprintf(i8*, i8*, ...)
+attributes #1 = { nounwind }