diff --git a/tests/component/updater_test.cpp b/tests/component/updater_test.cpp
index a859f11..bd1df55 100644
--- a/tests/component/updater_test.cpp
+++ b/tests/component/updater_test.cpp
@@ -16,7 +16,9 @@
 
 #include <string>
 
+#include <android-base/file.h>
 #include <android-base/properties.h>
+#include <android-base/test_utils.h>
 #include <gtest/gtest.h>
 
 #include "edify/expr.h"
@@ -97,3 +99,51 @@
     // sha1_check() expects at least one argument.
     expect(nullptr, "sha1_check()", kArgsParsingFailure);
 }
+
+TEST_F(UpdaterTest, file_getprop) {
+    // file_getprop() expects two arguments.
+    expect(nullptr, "file_getprop()", kArgsParsingFailure);
+    expect(nullptr, "file_getprop(\"arg1\")", kArgsParsingFailure);
+    expect(nullptr, "file_getprop(\"arg1\", \"arg2\", \"arg3\")", kArgsParsingFailure);
+
+    // File doesn't exist.
+    expect(nullptr, "file_getprop(\"/doesntexist\", \"key1\")", kFileGetPropFailure);
+
+    // Reject too large files (current limit = 65536).
+    TemporaryFile temp_file1;
+    std::string buffer(65540, '\0');
+    ASSERT_TRUE(android::base::WriteStringToFile(buffer, temp_file1.path));
+
+    // Read some keys.
+    TemporaryFile temp_file2;
+    std::string content("ro.product.name=tardis\n"
+                        "# comment\n\n\n"
+                        "ro.product.model\n"
+                        "ro.product.board =  magic \n");
+    ASSERT_TRUE(android::base::WriteStringToFile(content, temp_file2.path));
+
+    std::string script1("file_getprop(\"" + std::string(temp_file2.path) +
+                       "\", \"ro.product.name\")");
+    expect("tardis", script1.c_str(), kNoCause);
+
+    std::string script2("file_getprop(\"" + std::string(temp_file2.path) +
+                       "\", \"ro.product.board\")");
+    expect("magic", script2.c_str(), kNoCause);
+
+    // No match.
+    std::string script3("file_getprop(\"" + std::string(temp_file2.path) +
+                       "\", \"ro.product.wrong\")");
+    expect("", script3.c_str(), kNoCause);
+
+    std::string script4("file_getprop(\"" + std::string(temp_file2.path) +
+                       "\", \"ro.product.name=\")");
+    expect("", script4.c_str(), kNoCause);
+
+    std::string script5("file_getprop(\"" + std::string(temp_file2.path) +
+                       "\", \"ro.product.nam\")");
+    expect("", script5.c_str(), kNoCause);
+
+    std::string script6("file_getprop(\"" + std::string(temp_file2.path) +
+                       "\", \"ro.product.model\")");
+    expect("", script6.c_str(), kNoCause);
+}
diff --git a/updater/install.cpp b/updater/install.cpp
index efc96c4..19ba365 100644
--- a/updater/install.cpp
+++ b/updater/install.cpp
@@ -860,9 +860,13 @@
 // file_getprop(file, key)
 //
 //   interprets 'file' as a getprop-style file (key=value pairs, one
-//   per line. # comment lines,blank lines, lines without '=' ignored),
+//   per line. # comment lines, blank lines, lines without '=' ignored),
 //   and returns the value for 'key' (or "" if it isn't defined).
 Value* FileGetPropFn(const char* name, State* state, int argc, Expr* argv[]) {
+    if (argc != 2) {
+        return ErrorAbort(state, kArgsParsingFailure, "%s() expects 2 args, got %d", name, argc);
+    }
+
     std::vector<std::string> args;
     if (!ReadArgs(state, 2, argv, &args)) {
         return ErrorAbort(state, kArgsParsingFailure, "%s() Failed to parse the argument(s)", name);
@@ -876,11 +880,10 @@
                           filename.c_str(), strerror(errno));
     }
 
-#define MAX_FILE_GETPROP_SIZE    65536
-
+    constexpr off_t MAX_FILE_GETPROP_SIZE = 65536;
     if (st.st_size > MAX_FILE_GETPROP_SIZE) {
-        return ErrorAbort(state, kFileGetPropFailure, "%s too large for %s (max %d)",
-                          filename.c_str(), name, MAX_FILE_GETPROP_SIZE);
+        return ErrorAbort(state, kFileGetPropFailure, "%s too large for %s (max %lld)",
+                          filename.c_str(), name, static_cast<long long>(MAX_FILE_GETPROP_SIZE));
     }
 
     std::string buffer(st.st_size, '\0');
@@ -913,7 +916,7 @@
         }
 
         // trim whitespace between key and '='
-        std::string str = android::base::Trim(line.substr(0, equal_pos - 1));
+        std::string str = android::base::Trim(line.substr(0, equal_pos));
 
         // not the key we're looking for
         if (key != str) continue;