diff --git a/techlibs/achronix/synth_achronix.cc b/techlibs/achronix/synth_achronix.cc
index 1b48f426b..f8993de91 100644
--- a/techlibs/achronix/synth_achronix.cc
+++ b/techlibs/achronix/synth_achronix.cc
@@ -129,6 +129,7 @@ struct SynthAchronixPass : public ScriptPass {
     if (flatten && check_label("flatten", "(unless -noflatten)"))
       {
         run("proc");
+        run("check");
         run("flatten");
         run("tribuf -logic");
         run("deminout");
diff --git a/techlibs/analogdevices/synth_analogdevices.cc b/techlibs/analogdevices/synth_analogdevices.cc
index 00d2e18d6..aa27c78b6 100644
--- a/techlibs/analogdevices/synth_analogdevices.cc
+++ b/techlibs/analogdevices/synth_analogdevices.cc
@@ -277,8 +277,10 @@ struct SynthAnalogDevicesPass : public ScriptPass
 
 		if (check_label("prepare")) {
 			run("proc");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten", "(with '-flatten')");
+			}
 			if (active_design)
 				active_design->scratchpad_unset("tribuf.added_something");
 			run("tribuf -logic");
@@ -447,8 +449,10 @@ struct SynthAnalogDevicesPass : public ScriptPass
 
 		if (check_label("map_luts")) {
 			run("opt_expr -mux_undef -noclkinv");
-			if (flatten_before_abc)
+			if (flatten_before_abc) {
+				run("check");
 				run("flatten");
+			}
 			if (help_mode)
 				run("abc -luts 2:2,3,6:5[,10,20] [-dff] [-D 1]", "(option for '-nowidelut', '-dff', '-retime')");
 			else if (abc9) {
diff --git a/techlibs/anlogic/synth_anlogic.cc b/techlibs/anlogic/synth_anlogic.cc
index a03374fb0..5c7c0b532 100644
--- a/techlibs/anlogic/synth_anlogic.cc
+++ b/techlibs/anlogic/synth_anlogic.cc
@@ -156,6 +156,7 @@ struct SynthAnlogicPass : public ScriptPass
 		if (flatten && check_label("flatten", "(unless -noflatten)"))
 		{
 			run("proc");
+			run("check");
 			run("flatten");
 			run("tribuf -logic");
 			run("deminout");
diff --git a/techlibs/common/synth.cc b/techlibs/common/synth.cc
index 76f048495..00d884107 100644
--- a/techlibs/common/synth.cc
+++ b/techlibs/common/synth.cc
@@ -277,9 +277,10 @@ struct SynthPass : public ScriptPass {
 
 		if (check_label("coarse")) {
 			run("proc");
-			run("check");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten", "  (if -flatten)");
+			}
 			run("opt_expr");
 			run("opt_clean");
 			run("check");
diff --git a/techlibs/coolrunner2/synth_coolrunner2.cc b/techlibs/coolrunner2/synth_coolrunner2.cc
index 7ee1393be..1b30f51bc 100644
--- a/techlibs/coolrunner2/synth_coolrunner2.cc
+++ b/techlibs/coolrunner2/synth_coolrunner2.cc
@@ -132,6 +132,7 @@ struct SynthCoolrunner2Pass : public ScriptPass
 		if (flatten && check_label("flatten", "(unless -noflatten)"))
 		{
 			run("proc");
+			run("check");
 			run("flatten");
 			run("tribuf -logic");
 		}
diff --git a/techlibs/easic/synth_easic.cc b/techlibs/easic/synth_easic.cc
index 6c5df7beb..aea517cc5 100644
--- a/techlibs/easic/synth_easic.cc
+++ b/techlibs/easic/synth_easic.cc
@@ -142,6 +142,7 @@ struct SynthEasicPass : public ScriptPass
 		if (flatten && check_label("flatten", "(unless -noflatten)"))
 		{
 			run("proc");
+			run("check");
 			run("flatten");
 		}
 
diff --git a/techlibs/efinix/synth_efinix.cc b/techlibs/efinix/synth_efinix.cc
index ef245e755..14457c64b 100644
--- a/techlibs/efinix/synth_efinix.cc
+++ b/techlibs/efinix/synth_efinix.cc
@@ -148,6 +148,7 @@ struct SynthEfinixPass : public ScriptPass
 		if (flatten && check_label("flatten", "(unless -noflatten)"))
 		{
 			run("proc");
+			run("check");
 			run("flatten");
 			run("tribuf -logic");
 			run("deminout");
diff --git a/techlibs/fabulous/synth_fabulous.cc b/techlibs/fabulous/synth_fabulous.cc
index f74dc8e26..0074a52af 100644
--- a/techlibs/fabulous/synth_fabulous.cc
+++ b/techlibs/fabulous/synth_fabulous.cc
@@ -286,6 +286,7 @@ struct SynthPass : public ScriptPass
 		if (check_label("flatten", "(unless -noflatten)"))
 		{
 			if (flatten) {
+				run("check");
 				run("flatten");
 				run("tribuf -logic");
 				run("deminout");
diff --git a/techlibs/gatemate/synth_gatemate.cc b/techlibs/gatemate/synth_gatemate.cc
index 7726e7a15..409b07964 100644
--- a/techlibs/gatemate/synth_gatemate.cc
+++ b/techlibs/gatemate/synth_gatemate.cc
@@ -210,6 +210,7 @@ struct SynthGateMatePass : public ScriptPass
 		{
 			run("proc");
 			if (!noflatten) {
+				run("check");
 				run("flatten");
 			}
 			run("tribuf -logic");
diff --git a/techlibs/gowin/synth_gowin.cc b/techlibs/gowin/synth_gowin.cc
index ac028e2a6..d5ebdafea 100644
--- a/techlibs/gowin/synth_gowin.cc
+++ b/techlibs/gowin/synth_gowin.cc
@@ -265,8 +265,10 @@ struct SynthGowinPass : public ScriptPass
 		if (check_label("coarse"))
 		{
 			run("proc");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten", "(unless -noflatten)");
+			}
 			run("tribuf -logic");
 			run("deminout");
 			run("opt_expr");
diff --git a/techlibs/greenpak4/synth_greenpak4.cc b/techlibs/greenpak4/synth_greenpak4.cc
index fa52ecfc6..7f91d6332 100644
--- a/techlibs/greenpak4/synth_greenpak4.cc
+++ b/techlibs/greenpak4/synth_greenpak4.cc
@@ -144,6 +144,7 @@ struct SynthGreenPAK4Pass : public ScriptPass
 		if (flatten && check_label("flatten", "(unless -noflatten)"))
 		{
 			run("proc");
+			run("check");
 			run("flatten");
 			run("tribuf -logic");
 		}
diff --git a/techlibs/ice40/synth_ice40.cc b/techlibs/ice40/synth_ice40.cc
index 0a4144451..86189c848 100644
--- a/techlibs/ice40/synth_ice40.cc
+++ b/techlibs/ice40/synth_ice40.cc
@@ -309,6 +309,7 @@ struct SynthIce40Pass : public ScriptPass
 		if (check_label("flatten", "(unless -noflatten)"))
 		{
 			if (flatten) {
+				run("check");
 				run("flatten");
 				run("tribuf -logic");
 				run("deminout");
diff --git a/techlibs/intel/synth_intel.cc b/techlibs/intel/synth_intel.cc
index e02885cd0..0b0eb6ae9 100644
--- a/techlibs/intel/synth_intel.cc
+++ b/techlibs/intel/synth_intel.cc
@@ -198,9 +198,11 @@ struct SynthIntelPass : public ScriptPass {
 
 		if (check_label("coarse")) {
 			run("proc");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten", "(skip if -noflatten)");
-                        run("tribuf -logic");
+			}
+			run("tribuf -logic");
 			run("deminout");
 			run("opt_expr");
 			run("opt_clean");
diff --git a/techlibs/intel_alm/synth_intel_alm.cc b/techlibs/intel_alm/synth_intel_alm.cc
index 28852d7df..95dbb6e35 100644
--- a/techlibs/intel_alm/synth_intel_alm.cc
+++ b/techlibs/intel_alm/synth_intel_alm.cc
@@ -184,8 +184,10 @@ struct SynthIntelALMPass : public ScriptPass {
 
 		if (check_label("coarse")) {
 			run("proc");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten", "(skip if -noflatten)");
+			}
 			run("tribuf -logic");
 			run("deminout");
 			run("opt_expr");
diff --git a/techlibs/lattice/synth_lattice.cc b/techlibs/lattice/synth_lattice.cc
index 744beb650..382dae3d8 100644
--- a/techlibs/lattice/synth_lattice.cc
+++ b/techlibs/lattice/synth_lattice.cc
@@ -402,8 +402,10 @@ struct SynthLatticePass : public ScriptPass
 		if (check_label("coarse"))
 		{
 			run("proc");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten");
+			}
 			run("tribuf -logic");
 			run("deminout");
 			run("opt_expr");
diff --git a/techlibs/microchip/synth_microchip.cc b/techlibs/microchip/synth_microchip.cc
index e1d3c393a..218ed310f 100644
--- a/techlibs/microchip/synth_microchip.cc
+++ b/techlibs/microchip/synth_microchip.cc
@@ -267,8 +267,10 @@ struct SynthMicrochipPass : public ScriptPass {
 
 		if (check_label("prepare")) {
 			run("proc");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten", "(with '-flatten')");
+			}
 			if (active_design)
 				active_design->scratchpad_unset("tribuf.added_something");
 			run("tribuf -logic");
diff --git a/techlibs/nanoxplore/synth_nanoxplore.cc b/techlibs/nanoxplore/synth_nanoxplore.cc
index 3445ea1be..0b87c98c7 100644
--- a/techlibs/nanoxplore/synth_nanoxplore.cc
+++ b/techlibs/nanoxplore/synth_nanoxplore.cc
@@ -250,8 +250,10 @@ struct SynthNanoXplorePass : public ScriptPass
 		if (check_label("coarse"))
 		{
 			run("proc");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten", "(skip if -noflatten)");
+			}
 			run("tribuf -logic");
 			run("deminout");
 			run("opt_expr");
diff --git a/techlibs/quicklogic/synth_quicklogic.cc b/techlibs/quicklogic/synth_quicklogic.cc
index 1026dc233..e65be1c58 100644
--- a/techlibs/quicklogic/synth_quicklogic.cc
+++ b/techlibs/quicklogic/synth_quicklogic.cc
@@ -212,8 +212,10 @@ struct SynthQuickLogicPass : public ScriptPass {
 
 		if (check_label("prepare")) {
 			run("proc");
-			if (flatten)
+			if (flatten) {
+				run("check");
 				run("flatten", "(unless -noflatten)");
+			}
 			if (help_mode || family == "pp3") {
 				run("tribuf -logic", "                   (for pp3)");
 			}
diff --git a/techlibs/sf2/synth_sf2.cc b/techlibs/sf2/synth_sf2.cc
index ad335536b..7a7f87466 100644
--- a/techlibs/sf2/synth_sf2.cc
+++ b/techlibs/sf2/synth_sf2.cc
@@ -172,6 +172,7 @@ struct SynthSf2Pass : public ScriptPass
 		if (flatten && check_label("flatten", "(unless -noflatten)"))
 		{
 			run("proc");
+			run("check");
 			run("flatten");
 			run("tribuf -logic");
 			run("deminout");
diff --git a/techlibs/xilinx/synth_xilinx.cc b/techlibs/xilinx/synth_xilinx.cc
index c487206db..b08fbe499 100644
--- a/techlibs/xilinx/synth_xilinx.cc
+++ b/techlibs/xilinx/synth_xilinx.cc
@@ -355,8 +355,10 @@ struct SynthXilinxPass : public ScriptPass
 
 		if (check_label("prepare")) {
 			run("proc");
-			if (flatten || help_mode)
+			if (flatten || help_mode) {
+				run("check");
 				run("flatten", "(with '-flatten')");
+			}
 			if (active_design)
 				active_design->scratchpad_unset("tribuf.added_something");
 			run("tribuf -logic");
@@ -637,8 +639,10 @@ struct SynthXilinxPass : public ScriptPass
 
 		if (check_label("map_luts")) {
 			run("opt_expr -mux_undef -noclkinv");
-			if (flatten_before_abc)
+			if (flatten_before_abc) {
+				run("check");
 				run("flatten");
+			}
 			if (help_mode)
 				run("abc -luts 2:2,3,6:5[,10,20] [-dff] [-D 1]", "(option for '-nowidelut', '-dff', '-retime')");
 			else if (abc9) {