diff --git a/amaranth/build/plat.py b/amaranth/build/plat.py
index d132178..7b22735 100644
--- a/amaranth/build/plat.py
+++ b/amaranth/build/plat.py
@@ -276,6 +276,7 @@ class TemplatedPlatform(Platform):
 
     build_script_templates = {
         "build_{{name}}.sh": """
+            #!/bin/sh
             # {{autogenerated}}
             set -e{{verbose("x")}}
             {% for var in platform._all_toolchain_env_vars %}
diff --git a/amaranth/vendor/_intel.py b/amaranth/vendor/_intel.py
index 8f2ecc2..58f07eb 100644
--- a/amaranth/vendor/_intel.py
+++ b/amaranth/vendor/_intel.py
@@ -80,6 +80,7 @@ class IntelPlatform(TemplatedPlatform):
     quartus_file_templates = {
         **TemplatedPlatform.build_script_templates,
         "build_{{name}}.sh": r"""
+            #!/bin/sh
             # {{autogenerated}}
             {% for var in platform._all_toolchain_env_vars %}
             if [ -n "${{var}}" ]; then
diff --git a/amaranth/vendor/_lattice_ecp5.py b/amaranth/vendor/_lattice_ecp5.py
index 261ccbe..d75f629 100644
--- a/amaranth/vendor/_lattice_ecp5.py
+++ b/amaranth/vendor/_lattice_ecp5.py
@@ -182,6 +182,7 @@ class LatticeECP5Platform(TemplatedPlatform):
     _diamond_file_templates = {
         **TemplatedPlatform.build_script_templates,
         "build_{{name}}.sh": r"""
+            #!/bin/sh
             # {{autogenerated}}
             set -e{{verbose("x")}}
             if [ -z "$BASH" ] ; then exec /bin/bash "$0" "$@"; fi
diff --git a/amaranth/vendor/_lattice_ice40.py b/amaranth/vendor/_lattice_ice40.py
index 34f2363..a4e1bc2 100644
--- a/amaranth/vendor/_lattice_ice40.py
+++ b/amaranth/vendor/_lattice_ice40.py
@@ -175,6 +175,7 @@ class LatticeICE40Platform(TemplatedPlatform):
     _icecube2_file_templates = {
         **TemplatedPlatform.build_script_templates,
         "build_{{name}}.sh": r"""
+            #!/bin/sh
             # {{autogenerated}}
             set -e{{verbose("x")}}
             {% for var in platform._all_toolchain_env_vars %}
diff --git a/amaranth/vendor/_xilinx.py b/amaranth/vendor/_xilinx.py
index e7c884b..0f033e2 100644
--- a/amaranth/vendor/_xilinx.py
+++ b/amaranth/vendor/_xilinx.py
@@ -139,6 +139,7 @@ class XilinxPlatform(TemplatedPlatform):
     _vivado_file_templates = {
         **TemplatedPlatform.build_script_templates,
         "build_{{name}}.sh": r"""
+            #!/bin/sh
             # {{autogenerated}}
             set -e{{verbose("x")}}
             if [ -z "$BASH" ] ; then exec /bin/bash "$0" "$@"; fi
diff --git a/docs/changes.rst b/docs/changes.rst
index 34a251c..8dbb71a 100644
--- a/docs/changes.rst
+++ b/docs/changes.rst
@@ -35,6 +35,7 @@ Platform integration changes
 
 .. currentmodule:: amaranth.vendor
 
+* Added: ``build.sh``  begins with ``#!/bin/sh``.
 * Removed: (deprecated in 0.4) :mod:`vendor.intel`, :mod:`vendor.lattice_ecp5`, :mod:`vendor.lattice_ice40`, :mod:`vendor.lattice_machxo2_3l`, :mod:`vendor.quicklogic`, :mod:`vendor.xilinx`. (`RFC 18`_)