diff --git a/build/unix/Makefile.am b/build/unix/Makefile.am
index 17f39a4..b4b9cda 100644
--- a/build/unix/Makefile.am
+++ b/build/unix/Makefile.am
@@ -5,7 +5,6 @@ warningflags = \
         -Wextra \
         -Wshadow \
         -Wunused \
-        -Wmisleading-indentation \
         -Wnull-dereference \
         -Wvla \
         -Wstrict-aliasing \
@@ -31,7 +30,6 @@ warningflags += \
         -Wbool-conversion \
         -Wextra-semi \
         -Wnullable-to-nonnull-conversion \
-        -Wno-implicit-int-float-conversion \
         -Wno-unused-private-field \
         -Wno-unused-command-line-argument
 # -Wzero-as-null-pointer-constant
diff --git a/build/unix/configure.ac b/build/unix/configure.ac
index 0f04a18..65676fb 100644
--- a/build/unix/configure.ac
+++ b/build/unix/configure.ac
@@ -111,6 +111,10 @@ AS_IF(
     ]
 )
 
+AX_CHECK_COMPILE_FLAG([-Wmisleading-indentation]          , [COMPWARNFLAGS="$COMPWARNFLAGS -Wmisleading-indentation"]          , , [-Werror])
+# Clang only
+AX_CHECK_COMPILE_FLAG([-Wno-implicit-int-float-conversion], [COMPWARNFLAGS="$COMPWARNFLAGS -Wno-implicit-int-float-conversion"], , [-Werror])
+
 AC_SUBST([CXXSTD])
 AC_SUBST([EXTRA_CXXFLAGS])
 AC_SUBST([LDFLAGS])
diff --git a/src/ffft/FFTReal.hpp b/src/ffft/FFTReal.hpp
index 1493ff9..37c0ef0 100644
--- a/src/ffft/FFTReal.hpp
+++ b/src/ffft/FFTReal.hpp
@@ -371,11 +371,11 @@ void	FFTReal <DT>::init_trigo_lut ()
 			const long		level_len = 1L << (level - 1);
 			DataType	* const	level_ptr =
 				&_trigo_lut [get_trigo_level_index (level)];
-			const double	mul = PI / (level_len << 1);
+			const double	mul = PI / double (level_len << 1);
 
 			for (long i = 0; i < level_len; ++ i)
 			{
-				level_ptr [i] = static_cast <DataType> (cos (i * mul));
+				level_ptr [i] = static_cast <DataType> (cos (double (i) * mul));
 			}
 		}
 	}
@@ -396,7 +396,7 @@ void	FFTReal <DT>::init_trigo_osc ()
 			OscType &		osc = _trigo_osc [osc_cnt];
 
 			const long		len = 1L << (TRIGO_BD_LIMIT + osc_cnt);
-			const double	mul = (0.5 * PI) / len;
+			const double	mul = (0.5 * PI) / double (len);
 			osc.set_step (mul);
 		}
 	}