diff --git a/middle/tanya/memory/allocator.d b/middle/tanya/memory/allocator.d
index bde97d2..064ab37 100644
--- a/middle/tanya/memory/allocator.d
+++ b/middle/tanya/memory/allocator.d
@@ -101,7 +101,11 @@ mixin template DefaultAllocator()
      * Precondition: $(D_INLINECODE allocator_ !is null)
      */
     this(shared Allocator allocator) @nogc nothrow pure @safe
-    in (allocator !is null)
+    in
+    {
+        assert(allocator !is null);
+    }
+    do
     {
         this.allocator_ = allocator;
     }
@@ -115,7 +119,11 @@ mixin template DefaultAllocator()
      * Postcondition: $(D_INLINECODE allocator !is null)
      */
     @property shared(Allocator) allocator() @nogc nothrow pure @safe
-    out (allocator; allocator !is null)
+    out (allocator)
+    {
+        assert(allocator !is null);
+    }
+    do
     {
         if (allocator_ is null)
         {
@@ -126,7 +134,11 @@ mixin template DefaultAllocator()
 
     /// ditto
     @property shared(Allocator) allocator() const @nogc nothrow pure @trusted
-    out (allocator; allocator !is null)
+    out (allocator)
+    {
+        assert(allocator !is null);
+    }
+    do
     {
         if (allocator_ is null)
         {
@@ -162,7 +174,11 @@ private shared(Allocator) getAllocatorInstance() @nogc nothrow
  * Postcondition: $(D_INLINECODE allocator !is null).
  */
 @property shared(Allocator) defaultAllocator() @nogc nothrow pure @trusted
-out (allocator; allocator !is null)
+out (allocator)
+{
+    assert(allocator !is null);
+}
+do
 {
     return (cast(GetPureInstance!Allocator) &getAllocatorInstance)();
 }
@@ -176,7 +192,11 @@ out (allocator; allocator !is null)
  * Precondition: $(D_INLINECODE allocator !is null).
  */
 @property void defaultAllocator(shared(Allocator) allocator) @nogc nothrow @safe
-in (allocator !is null)
+in
+{
+    assert(allocator !is null);
+}
+do
 {
     .allocator = allocator;
 }
@@ -258,7 +278,11 @@ void dispose(T)(shared Allocator allocator, auto ref T p)
  */
 T make(T, A...)(shared Allocator allocator, auto ref A args)
 if (is(T == class))
-in (allocator !is null)
+in
+{
+    assert(allocator !is null);
+}
+do
 {
     auto mem = (() @trusted => allocator.allocate(stateSize!T))();
     if (mem is null)
@@ -290,7 +314,11 @@ in (allocator !is null)
  */
 T* make(T, A...)(shared Allocator allocator, auto ref A args)
 if (!isPolymorphicType!T && !isAssociativeArray!T && !isArray!T)
-in (allocator !is null)
+in
+{
+    assert(allocator !is null);
+}
+do
 {
     auto mem = (() @trusted => allocator.allocate(stateSize!T))();
     if (mem is null)
@@ -327,8 +355,12 @@ in (allocator !is null)
  *                           && n <= size_t.max / E.sizeof)
  */
 T make(T : E[], E)(shared Allocator allocator, size_t n)
-in (allocator !is null)
-in (n <= size_t.max / E.sizeof)
+in
+{
+    assert(allocator !is null);
+    assert(n <= size_t.max / E.sizeof);
+}
+do
 {
     auto ret = allocator.resize!E(null, n);
 
diff --git a/middle/tanya/memory/lifetime.d b/middle/tanya/memory/lifetime.d
index d5a028f..8a8cfe9 100644
--- a/middle/tanya/memory/lifetime.d
+++ b/middle/tanya/memory/lifetime.d
@@ -61,8 +61,15 @@ package(tanya) void destroyAllImpl(R, E)(R p)
  */
 T emplace(T, U, Args...)(void[] memory, U outer, auto ref Args args)
 if (!isAbstractClass!T && isInnerClass!T && is(typeof(T.outer) == U))
-in (memory.length >= stateSize!T)
-out (result; memory.ptr is (() @trusted => cast(void*) result)())
+in
+{
+    assert(memory.length >= stateSize!T);
+}
+out (result)
+{
+    assert(memory.ptr is (() @trusted => cast(void*) result)());
+}
+do
 {
     import tanya.memory.op : copy;
 
@@ -82,8 +89,15 @@ out (result; memory.ptr is (() @trusted => cast(void*) result)())
 /// ditto
 T emplace(T, Args...)(void[] memory, auto ref Args args)
 if (is(T == class) && !isAbstractClass!T && !isInnerClass!T)
-in (memory.length == stateSize!T)
-out (result; memory.ptr is (() @trusted => cast(void*) result)())
+in
+{
+    assert(memory.length == stateSize!T);
+}
+out (result)
+{
+    assert(memory.ptr is (() @trusted => cast(void*) result)());
+}
+do
 {
     import tanya.memory.op : copy;
 
@@ -128,8 +142,15 @@ out (result; memory.ptr is (() @trusted => cast(void*) result)())
 /// ditto
 T* emplace(T, Args...)(void[] memory, auto ref Args args)
 if (!isAggregateType!T && (Args.length <= 1))
-in (memory.length >= T.sizeof)
-out (result; memory.ptr is result)
+in
+{
+    assert(memory.length >= T.sizeof);
+}
+out (result)
+{
+    assert(memory.ptr is result);
+}
+do
 {
     auto result = (() @trusted => cast(T*) memory.ptr)();
     static if (Args.length == 1)
@@ -166,8 +187,15 @@ private void initializeOne(T)(ref void[] memory, ref T* result) @trusted
 /// ditto
 T* emplace(T, Args...)(void[] memory, auto ref Args args)
 if (!isPolymorphicType!T && isAggregateType!T)
-in (memory.length >= T.sizeof)
-out (result; memory.ptr is result)
+in
+{
+    assert(memory.length >= T.sizeof);
+}
+out (result)
+{
+    assert(memory.ptr is result);
+}
+do
 {
     auto result = (() @trusted => cast(T*) memory.ptr)();
 
@@ -291,7 +319,11 @@ private void deinitialize(bool zero, T)(ref T value)
  * Precondition: `&source !is &target`.
  */
 void moveEmplace(T)(ref T source, ref T target) @system
-in (&source !is &target, "Source and target must be different")
+in
+{
+    assert(&source !is &target, "Source and target must be different");
+}
+do
 {
     static if (is(T == struct) || isStaticArray!T)
     {
diff --git a/middle/tanya/memory/op.d b/middle/tanya/memory/op.d
index fdbff38..a41149b 100644
--- a/middle/tanya/memory/op.d
+++ b/middle/tanya/memory/op.d
@@ -36,9 +36,13 @@ private enum alignMask = size_t.sizeof - 1;
  * Precondition: $(D_INLINECODE source.length <= target.length).
  */
 void copy(const void[] source, void[] target) @nogc nothrow pure @trusted
-in (source.length <= target.length)
-in (source.length == 0 || source.ptr !is null)
-in (target.length == 0 || target.ptr !is null)
+in
+{
+    assert(source.length <= target.length);
+    assert(source.length == 0 || source.ptr !is null);
+    assert(target.length == 0 || target.ptr !is null);
+}
+do
 {
     memcpy(target.ptr, source.ptr, source.length);
 }
@@ -75,7 +79,11 @@ private template filledBytes(ubyte Byte, ubyte I = 0)
  *  memory = Memory block.
  */
 void fill(ubyte c = 0)(void[] memory) @trusted
-in (memory.length == 0 || memory.ptr !is null)
+in
+{
+    assert(memory.length == 0 || memory.ptr !is null);
+}
+do
 {
     memset(memory.ptr, c, memory.length);
 }
@@ -114,9 +122,13 @@ in (memory.length == 0 || memory.ptr !is null)
  * Precondition: $(D_INLINECODE source.length <= target.length).
  */
 void copyBackward(const void[] source, void[] target) @nogc nothrow pure @trusted
-in (source.length <= target.length)
-in (source.length == 0 || source.ptr !is null)
-in (target.length == 0 || target.ptr !is null)
+in
+{
+    assert(source.length <= target.length);
+    assert(source.length == 0 || source.ptr !is null);
+    assert(target.length == 0 || target.ptr !is null);
+}
+do
 {
     memmove(target.ptr, source.ptr, source.length);
 }
@@ -145,7 +157,11 @@ in (target.length == 0 || target.ptr !is null)
  */
 inout(void[]) find(return inout void[] haystack, ubyte needle)
 @nogc nothrow pure @trusted
-in (haystack.length == 0 || haystack.ptr !is null)
+in
+{
+    assert(haystack.length == 0 || haystack.ptr !is null);
+}
+do
 {
     auto length = haystack.length;
     const size_t needleWord = size_t.max * needle;
@@ -223,7 +239,11 @@ in (haystack.length == 0 || haystack.ptr !is null)
  */
 inout(char[]) findNullTerminated(return inout char[] haystack)
 @nogc nothrow pure @trusted
-in (haystack.length == 0 || haystack.ptr !is null)
+in
+{
+    assert(haystack.length == 0 || haystack.ptr !is null);
+}
+do
 {
     auto length = haystack.length;
     enum size_t highBits = filledBytes!(0x01, 0);
@@ -290,8 +310,12 @@ in (haystack.length == 0 || haystack.ptr !is null)
  *          $(D_KEYWORD false) otherwise.
  */
 bool equal(const void[] r1, const void[] r2) @nogc nothrow pure @trusted
-in (r1.length == 0 || r1.ptr !is null)
-in (r2.length == 0 || r2.ptr !is null)
+in
+{
+    assert(r1.length == 0 || r1.ptr !is null);
+    assert(r2.length == 0 || r2.ptr !is null);
+}
+do
 {
     return r1.length == r2.length && memcmp(r1.ptr, r2.ptr, r1.length) == 0;
 }
diff --git a/middle/tanya/memory/smartref.d b/middle/tanya/memory/smartref.d
index 7c14d4b..b6ec374 100644
--- a/middle/tanya/memory/smartref.d
+++ b/middle/tanya/memory/smartref.d
@@ -46,7 +46,11 @@ private final class RefCountedStore(T)
 
     size_t opUnary(string op)()
     if (op == "--" || op == "++")
-    in (this.counter > 0)
+    in
+    {
+        assert(this.counter > 0);
+    }
+    do
     {
         mixin("return " ~ op ~ "counter;");
     }
@@ -127,7 +131,11 @@ struct RefCounted(T)
 
     /// ditto
     this(shared Allocator allocator)
-    in (allocator !is null)
+    in
+    {
+        assert(allocator !is null);
+    }
+    do
     {
         this.allocator_ = allocator;
     }
@@ -231,7 +239,11 @@ struct RefCounted(T)
      * Precondition: $(D_INLINECODE cound > 0).
      */
     inout(Payload!T) get() inout
-    in (count > 0, "Attempted to access an uninitialized reference")
+    in
+    {
+        assert(count > 0, "Attempted to access an uninitialized reference");
+    }
+    do
     {
         return this.storage.payload;
     }
@@ -321,7 +333,11 @@ struct RefCounted(T)
 RefCounted!T refCounted(T, A...)(shared Allocator allocator, auto ref A args)
 if (!is(T == interface) && !isAbstractClass!T
  && !isAssociativeArray!T && !isArray!T)
-in (allocator !is null)
+in
+{
+    assert(allocator !is null);
+}
+do
 {
     auto rc = typeof(return)(allocator);
 
@@ -361,8 +377,12 @@ in (allocator !is null)
  */
 RefCounted!T refCounted(T : E[], E)(shared Allocator allocator, size_t size)
 @trusted
-in (allocator !is null)
-in (size <= size_t.max / E.sizeof)
+in
+{
+    assert(allocator !is null);
+    assert(size <= size_t.max / E.sizeof);
+}
+do
 {
     return RefCounted!T(allocator.make!T(size), allocator);
 }
@@ -423,7 +443,11 @@ struct Unique(T)
 
     /// ditto
     this(shared Allocator allocator)
-    in (allocator !is null)
+    in
+    {
+        assert(allocator !is null);
+    }
+    do
     {
         this.allocator_ = allocator;
     }
@@ -604,7 +628,11 @@ struct Unique(T)
 Unique!T unique(T, A...)(shared Allocator allocator, auto ref A args)
 if (!is(T == interface) && !isAbstractClass!T
  && !isAssociativeArray!T && !isArray!T)
-in (allocator !is null)
+in
+{
+    assert(allocator !is null);
+}
+do
 {
     auto payload = allocator.make!(T, A)(args);
     return Unique!T(payload, allocator);
@@ -627,8 +655,12 @@ in (allocator !is null)
  */
 Unique!T unique(T : E[], E)(shared Allocator allocator, size_t size)
 @trusted
-in (allocator !is null)
-in (size <= size_t.max / E.sizeof)
+in
+{
+    assert(allocator !is null);
+    assert(size <= size_t.max / E.sizeof);
+}
+do
 {
     auto payload = allocator.resize!E(null, size);
     return Unique!T(payload, allocator);
diff --git a/source/tanya/math/random.d b/source/tanya/math/random.d
index ae199f6..6ee4300 100644
--- a/source/tanya/math/random.d
+++ b/source/tanya/math/random.d
@@ -91,11 +91,7 @@ abstract class EntropySource
      * Postcondition: Returned length is less than or equal to
      *                $(D_PARAM output) length.
      */
-    Nullable!ubyte poll(out ubyte[maxGather] output) @nogc
-    out (length)
-    {
-        assert(length.isNull || length.get <= maxGather);
-    }
+    Nullable!ubyte poll(out ubyte[maxGather] output) @nogc;
 }
 
 version (CRuntime_Bionic)
@@ -156,6 +152,11 @@ version (linux)
          *          or nothing on error.
          */
         override Nullable!ubyte poll(out ubyte[maxGather] output) @nogc nothrow
+        out (length)
+        {
+            assert(length.isNull || length.get <= maxGather);
+        }
+        do
         {
             // int getrandom(void *buf, size_t buflen, unsigned int flags);
             import mir.linux._asm.unistd : NR_getrandom;
@@ -208,6 +209,11 @@ else version (SecureARC4Random)
          */
         override Nullable!ubyte poll(out ubyte[maxGather] output)
         @nogc nothrow @safe
+        out (length)
+        {
+            assert(length.isNull || length.get <= maxGather);
+        }
+        do
         {
             (() @trusted => arc4random_buf(output.ptr, output.length))();
             return Nullable!ubyte(cast(ubyte) (output.length));
@@ -316,6 +322,11 @@ else version (Windows)
          */
         override Nullable!ubyte poll(out ubyte[maxGather] output)
         @nogc nothrow @safe
+        out (length)
+        {
+            assert(length.isNull || length.get <= maxGather);
+        }
+        do
         {
             Nullable!ubyte ret;
 
diff --git a/source/tanya/range/array.d b/source/tanya/range/array.d
index 6104a91..bd47fb9 100644
--- a/source/tanya/range/array.d
+++ b/source/tanya/range/array.d
@@ -133,7 +133,7 @@ do
  *
  * Precondition: $(D_INLINECODE array.length > 0).
  */
-void popFront(T)(scope ref inout(T)[] array)
+void popFront(T)(ref inout(T)[] array)
 in
 {
     assert(array.length > 0);
@@ -144,7 +144,7 @@ do
 }
 
 /// ditto
-void popBack(T)(scope ref inout(T)[] array)
+void popBack(T)(ref inout(T)[] array)
 in
 {
     assert(array.length > 0);
diff --git a/source/tanya/typecons.d b/source/tanya/typecons.d
index d1402cf..5e570f6 100644
--- a/source/tanya/typecons.d
+++ b/source/tanya/typecons.d
@@ -396,7 +396,7 @@ if (isTypeTuple!Specs && NoDuplicates!Specs.length == Specs.length)
          * Returns: $(D_KEYWORD true) if this $(D_PSYMBOL Variant) is equal to
          *          $(D_PARAM that), $(D_KEYWORD false) otherwise.
          */
-        bool opEquals()(auto ref inout Variant that) inout
+        bool opEquals()(auto ref inout(Variant) that) inout
         {
             if (this.tag != that.tag)
             {
diff --git a/test/tanya/test/stub.d b/test/tanya/test/stub.d
index 07f65c1..99630e6 100644
--- a/test/tanya/test/stub.d
+++ b/test/tanya/test/stub.d
@@ -146,7 +146,11 @@ mixin template InputRangeStub(E = int)
     }
 
     void popFront() @nogc nothrow pure @safe
-    in (!empty)
+    in
+    {
+        assert(!empty);
+    }
+    do
     {
         static if (!infinite)
         {
@@ -157,7 +161,11 @@ mixin template InputRangeStub(E = int)
     static if (withLvalueElements)
     {
         ref E front() @nogc nothrow pure @safe
-        in (!empty)
+        in
+        {
+            assert(!empty);
+        }
+        do
         {
             return *this.element;
         }
@@ -165,7 +173,11 @@ mixin template InputRangeStub(E = int)
     else
     {
         E front() @nogc nothrow pure @safe
-        in (!empty)
+        in
+        {
+            assert(!empty);
+        }
+        do
         {
             return E.init;
         }
@@ -216,7 +228,11 @@ mixin template BidirectionalRangeStub(E = int)
     mixin ForwardRangeStub!E;
 
     void popBack() @nogc nothrow pure @safe
-    in (!empty)
+    in
+    {
+        assert(!empty);
+    }
+    do
     {
         static if (!infinite)
         {
@@ -227,7 +243,11 @@ mixin template BidirectionalRangeStub(E = int)
     static if (withLvalueElements)
     {
         ref E back() @nogc nothrow pure @safe
-        in (!empty)
+        in
+        {
+            assert(!empty);
+        }
+        do
         {
             return *this.element;
         }
@@ -235,7 +255,11 @@ mixin template BidirectionalRangeStub(E = int)
     else
     {
         E back() @nogc nothrow pure @safe
-        in (!empty)
+        in
+        {
+            assert(!empty);
+        }
+        do
         {
             return E.init;
         }
diff --git a/tests/tanya/algorithm/tests/mutation.d b/tests/tanya/algorithm/tests/mutation.d
index 19ab636..4403dd7 100644
--- a/tests/tanya/algorithm/tests/mutation.d
+++ b/tests/tanya/algorithm/tests/mutation.d
@@ -39,7 +39,11 @@ import tanya.test.stub;
         int value;
 
         void opCall(int value) @nogc nothrow pure @safe
-        in (this.value == 0)
+        in
+        {
+            assert(this.value == 0);
+        }
+        do
         {
             this.value = value;
         }
diff --git a/tests/tanya/range/tests/adapter.d b/tests/tanya/range/tests/adapter.d
index 4ebffab..cdd90a1 100644
--- a/tests/tanya/range/tests/adapter.d
+++ b/tests/tanya/range/tests/adapter.d
@@ -12,18 +12,6 @@ private struct Container
     }
 }
 
-// Broken test because of the issue #20006.
-@nogc nothrow pure @safe unittest
-{
-    auto func()()
-    {
-        Container container;
-        return backInserter(container);
-    }
-    // static assert(!is(typeof(func!())));
-    static assert(is(typeof(func!())));
-}
-
 @nogc nothrow pure @safe unittest
 {
     Container container;