diff --git a/clang/lib/AST/Interp/Integral.h b/clang/lib/AST/Interp/Integral.h
--- a/clang/lib/AST/Interp/Integral.h
+++ b/clang/lib/AST/Interp/Integral.h
@@ -94,6 +94,7 @@
   explicit operator unsigned() const { return V; }
   explicit operator int64_t() const { return V; }
   explicit operator uint64_t() const { return V; }
+  explicit operator int32_t() const { return V; }
 
   APSInt toAPSInt() const {
     return APSInt(APInt(Bits, static_cast<uint64_t>(V), Signed), !Signed);
diff --git a/clang/lib/AST/Interp/InterpBuiltin.cpp b/clang/lib/AST/Interp/InterpBuiltin.cpp
--- a/clang/lib/AST/Interp/InterpBuiltin.cpp
+++ b/clang/lib/AST/Interp/InterpBuiltin.cpp
@@ -32,6 +32,30 @@
   return R;
 }
 
+/// Pushes \p Val to the stack, as a target-dependent 'int'.
+static void pushInt(InterpState &S, int32_t Val) {
+  const TargetInfo &TI = S.getCtx().getTargetInfo();
+  unsigned IntWidth = TI.getIntWidth();
+
+  if (IntWidth == 32)
+    S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Val));
+  else if (IntWidth == 16)
+    S.Stk.push<Integral<16, true>>(Integral<16, true>::from(Val));
+  else
+    llvm_unreachable("Int isn't 16 or 32 bit?");
+}
+
+static bool retInt(InterpState &S, CodePtr OpPC, APValue &Result) {
+  const TargetInfo &TI = S.getCtx().getTargetInfo();
+  unsigned IntWidth = TI.getIntWidth();
+
+  if (IntWidth == 32)
+    return Ret<PT_Sint32>(S, OpPC, Result);
+  else if (IntWidth == 16)
+    return Ret<PT_Sint16>(S, OpPC, Result);
+  llvm_unreachable("Int isn't 16 or 32 bit?");
+}
+
 static bool interp__builtin_strcmp(InterpState &S, CodePtr OpPC,
                                    const InterpFrame *Frame) {
   const Pointer &A = getParam<Pointer>(Frame, 0);
@@ -67,7 +91,7 @@
       break;
   }
 
-  S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Result));
+  pushInt(S, Result);
   return true;
 }
 
@@ -200,7 +224,7 @@
                                   const InterpFrame *Frame, const Function *F) {
   const Floating &Arg = S.Stk.peek<Floating>();
 
-  S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Arg.isNan()));
+  pushInt(S, Arg.isNan());
   return true;
 }
 
@@ -211,10 +235,9 @@
   bool IsInf = Arg.isInf();
 
   if (CheckSign)
-    S.Stk.push<Integral<32, true>>(
-        Integral<32, true>::from(IsInf ? (Arg.isNegative() ? -1 : 1) : 0));
+    pushInt(S, IsInf ? (Arg.isNegative() ? -1 : 1) : 0);
   else
-    S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Arg.isInf()));
+    pushInt(S, Arg.isInf());
   return true;
 }
 
@@ -223,7 +246,7 @@
                                      const Function *F) {
   const Floating &Arg = S.Stk.peek<Floating>();
 
-  S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Arg.isFinite()));
+  pushInt(S, Arg.isFinite());
   return true;
 }
 
@@ -232,7 +255,7 @@
                                      const Function *F) {
   const Floating &Arg = S.Stk.peek<Floating>();
 
-  S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Arg.isNormal()));
+  pushInt(S, Arg.isNormal());
   return true;
 }
 
@@ -249,12 +272,12 @@
 
   int32_t Result =
       static_cast<int32_t>((F.classify() & FPClassArg).getZExtValue());
-  S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Result));
+  pushInt(S, Result);
 
   return true;
 }
 
-/// Five int32 values followed by one floating value.
+/// Five int values followed by one floating value.
 static bool interp__builtin_fpclassify(InterpState &S, CodePtr OpPC,
                                        const InterpFrame *Frame,
                                        const Function *Func) {
@@ -280,8 +303,9 @@
   unsigned Offset = align(primSize(PT_Float)) +
                     ((1 + (4 - Index)) * align(primSize(PT_Sint32)));
 
+  // FIXME: The size of the value we're peeking here is target-dependent.
   const Integral<32, true> &I = S.Stk.peek<Integral<32, true>>(Offset);
-  S.Stk.push<Integral<32, true>>(I);
+  pushInt(S, static_cast<int32_t>(I));
   return true;
 }
 
@@ -312,7 +336,7 @@
     return RetVoid(S, OpPC, Dummy);
   case Builtin::BI__builtin_strcmp:
     if (interp__builtin_strcmp(S, OpPC, Frame))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
+      return retInt(S, OpPC, Dummy);
     break;
   case Builtin::BI__builtin_nan:
   case Builtin::BI__builtin_nanf:
@@ -372,34 +396,34 @@
 
   case Builtin::BI__builtin_isnan:
     if (interp__builtin_isnan(S, OpPC, Frame, F))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
+      return retInt(S, OpPC, Dummy);
     break;
 
   case Builtin::BI__builtin_isinf:
     if (interp__builtin_isinf(S, OpPC, Frame, F, /*Sign=*/false))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
+      return retInt(S, OpPC, Dummy);
     break;
 
   case Builtin::BI__builtin_isinf_sign:
     if (interp__builtin_isinf(S, OpPC, Frame, F, /*Sign=*/true))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
+      return retInt(S, OpPC, Dummy);
     break;
 
   case Builtin::BI__builtin_isfinite:
     if (interp__builtin_isfinite(S, OpPC, Frame, F))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
+      return retInt(S, OpPC, Dummy);
     break;
   case Builtin::BI__builtin_isnormal:
     if (interp__builtin_isnormal(S, OpPC, Frame, F))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
+      return retInt(S, OpPC, Dummy);
     break;
   case Builtin::BI__builtin_isfpclass:
     if (interp__builtin_isfpclass(S, OpPC, Frame, F, Call))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
+      return retInt(S, OpPC, Dummy);
     break;
   case Builtin::BI__builtin_fpclassify:
     if (interp__builtin_fpclassify(S, OpPC, Frame, F))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
+      return retInt(S, OpPC, Dummy);
     break;
 
   case Builtin::BI__builtin_fabs:
diff --git a/clang/test/AST/Interp/builtin-functions.cpp b/clang/test/AST/Interp/builtin-functions.cpp
--- a/clang/test/AST/Interp/builtin-functions.cpp
+++ b/clang/test/AST/Interp/builtin-functions.cpp
@@ -2,6 +2,8 @@
 // RUN: %clang_cc1 -verify=ref %s -Wno-constant-evaluated
 // RUN: %clang_cc1 -std=c++20 -fexperimental-new-constant-interpreter %s -verify
 // RUN: %clang_cc1 -std=c++20 -verify=ref %s -Wno-constant-evaluated
+// RUN: %clang_cc1 -triple avr -std=c++20 -fexperimental-new-constant-interpreter %s -verify
+// RUN: %clang_cc1 -triple avr -std=c++20 -verify=ref %s -Wno-constant-evaluated
 
 
 namespace strcmp {
@@ -96,10 +98,12 @@
   char isfpclass_pos_1    [!__builtin_isfpclass(1.0f, 0x0008) ? 1 : -1]; // fcNegNormal
   char isfpclass_pos_2    [__builtin_isfpclass(1.0L, 0x01F8) ? 1 : -1]; // fcFinite
   char isfpclass_pos_3    [!__builtin_isfpclass(1.0, 0x0003) ? 1 : -1]; // fcSNan|fcQNan
+#ifndef __AVR__
   char isfpclass_pdenorm_0[__builtin_isfpclass(1.0e-40f, 0x0080) ? 1 : -1]; // fcPosSubnormal
   char isfpclass_pdenorm_1[__builtin_isfpclass(1.0e-310, 0x01F8) ? 1 : -1]; // fcFinite
   char isfpclass_pdenorm_2[!__builtin_isfpclass(1.0e-40f, 0x003C) ? 1 : -1]; // fcNegative
   char isfpclass_pdenorm_3[!__builtin_isfpclass(1.0e-310, 0x0207) ? 1 : -1]; // ~fcFinite
+#endif
   char isfpclass_pzero_0  [__builtin_isfpclass(0.0f, 0x0060) ? 1 : -1]; // fcZero
   char isfpclass_pzero_1  [__builtin_isfpclass(0.0, 0x01F8) ? 1 : -1]; // fcFinite
   char isfpclass_pzero_2  [!__builtin_isfpclass(0.0L, 0x0020) ? 1 : -1]; // fcNegZero
@@ -109,9 +113,11 @@
   char isfpclass_nzero_2  [!__builtin_isfpclass(-0.0L, 0x0040) ? 1 : -1]; // fcPosZero
   char isfpclass_nzero_3  [!__builtin_isfpclass(-0.0, 0x0003) ? 1 : -1]; // fcNan
   char isfpclass_ndenorm_0[__builtin_isfpclass(-1.0e-40f, 0x0010) ? 1 : -1]; // fcNegSubnormal
-  char isfpclass_ndenorm_1[__builtin_isfpclass(-1.0e-310, 0x01F8) ? 1 : -1]; // fcFinite
   char isfpclass_ndenorm_2[!__builtin_isfpclass(-1.0e-40f, 0x03C0) ? 1 : -1]; // fcPositive
+#ifndef __AVR__
+  char isfpclass_ndenorm_1[__builtin_isfpclass(-1.0e-310, 0x01F8) ? 1 : -1]; // fcFinite
   char isfpclass_ndenorm_3[!__builtin_isfpclass(-1.0e-310, 0x0207) ? 1 : -1]; // ~fcFinite
+#endif
   char isfpclass_neg_0    [__builtin_isfpclass(-1.0, 0x0008) ? 1 : -1]; // fcNegNormal
   char isfpclass_neg_1    [!__builtin_isfpclass(-1.0f, 0x00100) ? 1 : -1]; // fcPosNormal
   char isfpclass_neg_2    [__builtin_isfpclass(-1.0L, 0x01F8) ? 1 : -1]; // fcFinite
@@ -136,9 +142,11 @@
   char classify_inf     [__builtin_fpclassify(-1, +1, -1, -1, -1, __builtin_inf())];
   char classify_neg_inf [__builtin_fpclassify(-1, +1, -1, -1, -1, -__builtin_inf())];
   char classify_normal  [__builtin_fpclassify(-1, -1, +1, -1, -1, 1.539)];
+#ifndef __AVR__
   char classify_normal2 [__builtin_fpclassify(-1, -1, +1, -1, -1, 1e-307)];
   char classify_denorm  [__builtin_fpclassify(-1, -1, -1, +1, -1, 1e-308)];
   char classify_denorm2 [__builtin_fpclassify(-1, -1, -1, +1, -1, -1e-308)];
+#endif
   char classify_zero    [__builtin_fpclassify(-1, -1, -1, -1, +1, 0.0)];
   char classify_neg_zero[__builtin_fpclassify(-1, -1, -1, -1, +1, -0.0)];
   char classify_subnorm [__builtin_fpclassify(-1, -1, -1, +1, -1, 1.0e-38f)];