diff --git a/components/partition_table/check_sizes.py b/components/partition_table/check_sizes.py
index 8e9efac102..2045155143 100755
--- a/components/partition_table/check_sizes.py
+++ b/components/partition_table/check_sizes.py
@@ -77,8 +77,12 @@ def check_partition(ptype, subtype, partition_table_file, bin_file):  # type: (s
     smallest_size = min(p.size for p in partitions)
     if smallest_size >= bin_size:
         free_size = smallest_size - bin_size
-        print('{} binary size {:#x} bytes. Smallest {} partition is {:#x} bytes. {:#x} bytes ({}%) free.'.format(
-            bin_name, bin_size, ptype_str, smallest_size, free_size, round(free_size * 100 / smallest_size)))
+        free_size_relative = free_size / smallest_size
+        print('{} binary size {:#x} bytes. Smallest {} partition is {:#x} bytes. {:#x} bytes ({:.0%}) free.'.format(
+            bin_name, bin_size, ptype_str, smallest_size, free_size, free_size_relative))
+        free_size_relative_critical = 0.05
+        if free_size_relative < free_size_relative_critical:
+            print('Warning: The smallest {} partition is nearly full ({:.0%} free space left)!'.format(ptype_str, free_size_relative))
         return
 
     too_small_partitions = [p for p in partitions if p.size < bin_size]
diff --git a/tools/ci/test_build_system_cmake.sh b/tools/ci/test_build_system_cmake.sh
index 58930858e6..de456fa4b3 100755
--- a/tools/ci/test_build_system_cmake.sh
+++ b/tools/ci/test_build_system_cmake.sh
@@ -814,6 +814,15 @@ endmenu\n" >> ${IDF_PATH}/Kconfig
     ( idf.py build 2>&1 | grep "does not fit in configured flash size 1MB" ) || failure "Build didn't fail with expected flash size failure message"
     mv sdkconfig.bak sdkconfig
 
+    print_status "Warning is given if smallest partition is nearly full"
+    clean_build_dir
+    cp ${IDF_PATH}/components/partition_table/partitions_singleapp.csv partitions.csv
+    ${SED} -i "s/factory,  app,  factory, ,        1M/factory,  app,  factory, ,        170K/" partitions.csv
+    echo "CONFIG_PARTITION_TABLE_CUSTOM=y" > sdkconfig
+    ( idf.py build 2>&1 | grep "partition is nearly full" ) || failure "No warning for nearly full smallest partition was given when the condition is fulfilled"
+    rm -f partitions.csv sdkconfig
+    ( idf.py build 2>&1 | grep "partition is nearly full" ) && failure "Warning for nearly full smallest partition was given when the condition is not fulfilled"
+
     print_status "Flash size is correctly set in the bootloader image header"
     # Build with the default 2MB setting
     rm sdkconfig