diff --git a/bin/omarchy-webapp-install b/bin/omarchy-webapp-install
index 308f8841..ebf6ea39 100755
--- a/bin/omarchy-webapp-install
+++ b/bin/omarchy-webapp-install
@@ -54,13 +54,21 @@ normalize_webapp_url() {
   printf '%s' "$url"
 }
 
+# A space in the URL becomes a second desktop Exec argument, which
+# omarchy-launch-webapp hands to the browser as another URL to open. Schemes
+# are case-insensitive.
 require_http_url() {
   local url=$1
-  if [[ $url =~ ^https?:// ]]; then
-    return 0
+
+  if [[ $url =~ [[:space:]] ]]; then
+    echo "Error: web app URL must not contain whitespace." >&2
+    exit 1
+  fi
+
+  if [[ ! ${url,,} =~ ^https?:// ]]; then
+    echo "Error: web app URL must be http or https." >&2
+    exit 1
   fi
-  echo "Error: web app URL must be http or https." >&2
-  exit 1
 }
 
 fetch_site_icon() {
@@ -91,6 +99,7 @@ if (( $# < 3 )); then
   APP_NAME=$(gum input --prompt "Name> " --placeholder "My favorite web app")
   APP_URL=$(gum input --prompt "URL> " --placeholder "https://example.com")
   APP_URL=$(normalize_webapp_url "$APP_URL")
+  require_http_url "$APP_URL"
 
   # Try to fetch the site's icon automatically first.
   mkdir -p "$ICON_DIR"
@@ -108,6 +117,7 @@ if (( $# < 3 )); then
 else
   APP_NAME="$1"
   APP_URL=$(normalize_webapp_url "$2")
+  require_http_url "$APP_URL"
   ICON_REF="$3"
   CUSTOM_EXEC="$4" # Optional custom exec command
   MIME_TYPES="$5"  # Optional mime types
@@ -120,8 +130,6 @@ if [[ -z $APP_NAME || -z $APP_URL ]]; then
   exit 1
 fi
 
-require_http_url "$APP_URL"
-
 if [[ -z $ICON_REF ]]; then
   ICON_VALUE=$(safe_icon_name "$APP_NAME")
   mkdir -p "$ICON_DIR"
diff --git a/test/shell.d/webapp-install-test.sh b/test/shell.d/webapp-install-test.sh
index f436a2d3..f845d928 100644
--- a/test/shell.d/webapp-install-test.sh
+++ b/test/shell.d/webapp-install-test.sh
@@ -58,3 +58,63 @@ for url in "javascript:alert(1)" "file:///etc/passwd" "data:text/html,hi" "ftp:/
   [[ ! -e $(desktop_for Bad) ]] || fail "webapp install does not write a desktop file for '$url'"
 done
 pass "webapp install refuses non-http(s) URLs"
+
+# A leading space keeps the URL out of the scheme test, and the desktop Exec
+# field splits it back into two arguments the browser both opens.
+for url in " javascript:alert(1)" " file:///etc/passwd" "https://example.com data:text/html,hi"; do
+  if install_webapp "Sneak" "$url" "webapp" >"$tmpdir/out" 2>"$tmpdir/err"; then
+    fail "webapp install refuses whitespace in '$url'" "$(cat "$(desktop_for Sneak)")"
+  fi
+  grep -Fq 'must not contain whitespace' "$tmpdir/err" ||
+    fail "webapp install names the whitespace refusal for '$url'" "$(cat "$tmpdir/err")"
+  [[ ! -e $(desktop_for Sneak) ]] || fail "webapp install writes no desktop file for '$url'"
+done
+pass "webapp install refuses a URL carrying whitespace"
+
+# Schemes are case-insensitive, and HTTPS://example.com installed before the
+# scheme test existed.
+if install_webapp "Upper" "HTTPS://example.com" "webapp" >"$tmpdir/out" 2>"$tmpdir/err"; then
+  :
+else
+  fail "webapp install accepts an uppercase scheme" "$(cat "$tmpdir/err")"
+fi
+grep -Fxq 'Exec=omarchy-launch-webapp HTTPS://example.com' "$(desktop_for Upper)" ||
+  fail "webapp install keeps the uppercase scheme" "$(cat "$(desktop_for Upper)")"
+pass "webapp install accepts an uppercase http scheme"
+
+# The interactive prompt fetches the site's icon, so a refused URL must be
+# refused before anything dereferences it.
+stubs="$tmpdir/stubs"
+mkdir -p "$stubs"
+
+cat >"$stubs/gum" <<'GUM'
+#!/bin/bash
+count=$(cat "$GUM_COUNT" 2>/dev/null || echo 0)
+count=$((count + 1))
+printf '%s\n' "$count" >"$GUM_COUNT"
+sed -n "${count}p" "$GUM_ANSWERS"
+GUM
+
+cat >"$stubs/curl" <<'CURL'
+#!/bin/bash
+printf '%s\n' "$*" >>"$CURL_LOG"
+exit 1
+CURL
+
+chmod +x "$stubs/gum" "$stubs/curl"
+
+printf 'Evil\nfile:///etc/passwd\n' >"$tmpdir/answers"
+: >"$tmpdir/gum-count"
+: >"$tmpdir/curl-log"
+
+if GUM_ANSWERS="$tmpdir/answers" GUM_COUNT="$tmpdir/gum-count" CURL_LOG="$tmpdir/curl-log" \
+  PATH="$stubs:$PATH" HOME="$home" "$ROOT/bin/omarchy-webapp-install" \
+  >"$tmpdir/out" 2>"$tmpdir/err"; then
+  fail "interactive webapp install refuses a file: URL" "$(cat "$tmpdir/out")"
+fi
+grep -Fq 'must be http or https' "$tmpdir/err" ||
+  fail "interactive webapp install names the scheme refusal" "$(cat "$tmpdir/err")"
+[[ ! -s $tmpdir/curl-log ]] ||
+  fail "interactive webapp install refuses before fetching the URL" "$(cat "$tmpdir/curl-log")"
+[[ ! -e $(desktop_for Evil) ]] || fail "interactive webapp install writes no desktop file"
+pass "interactive webapp install refuses a bad URL before fetching it"