diff --git a/docs/source/nnls_modeling.rst b/docs/source/nnls_modeling.rst
index 19384a6..911bd63 100644
--- a/docs/source/nnls_modeling.rst
+++ b/docs/source/nnls_modeling.rst
@@ -919,7 +919,7 @@
            local_parameterizations, numeric_diff_options);
        GradientCheckResults results;
        if (!gradient_checker.Probe(parameter_blocks.data(), 1e-9, &results) {
-         LOG(ERROR) << "An error has occured:\n" << results.error_log;
+         LOG(ERROR) << "An error has occurred:\n" << results.error_log;
        }
 
 
diff --git a/internal/ceres/evaluator_test.cc b/internal/ceres/evaluator_test.cc
index 7c234f3..48dc78a 100644
--- a/internal/ceres/evaluator_test.cc
+++ b/internal/ceres/evaluator_test.cc
@@ -252,7 +252,7 @@
   // the jacobian evaluation, but requires explicit handling in the evaluators.
   // At one point the compressed row evaluator had a bug that went undetected
   // for a long time, since by chance most users added parameters to the problem
-  // in the same order that they occured as parameters to a cost function.
+  // in the same order that they occurred as parameters to a cost function.
   problem.AddResidualBlock(new ParameterIgnoringCostFunction<1, 3, 4, 3, 2>,
                            NULL,
                            z, y, x);
diff --git a/internal/ceres/gradient_checking_cost_function.h b/internal/ceres/gradient_checking_cost_function.h
index f137349..497f8e2 100644
--- a/internal/ceres/gradient_checking_cost_function.h
+++ b/internal/ceres/gradient_checking_cost_function.h
@@ -54,7 +54,7 @@
   // then return SOLVER_ABORT.
   virtual CallbackReturnType operator()(const IterationSummary& summary);
 
-  // Notify this that a gradient error has occured (thread safe).
+  // Notify this that a gradient error has occurred (thread safe).
   void SetGradientErrorDetected(std::string& error_log);
 
   // Retrieve error status (not thread safe).
diff --git a/internal/ceres/suitesparse.cc b/internal/ceres/suitesparse.cc
index 200daa2..2018877 100644
--- a/internal/ceres/suitesparse.cc
+++ b/internal/ceres/suitesparse.cc
@@ -280,7 +280,7 @@
       *message = "CHOLMOD failure: Out of memory.";
       return LINEAR_SOLVER_FATAL_ERROR;
     case CHOLMOD_TOO_LARGE:
-      *message = "CHOLMOD failure: Integer overflow occured.";
+      *message = "CHOLMOD failure: Integer overflow occurred.";
       return LINEAR_SOLVER_FATAL_ERROR;
     case CHOLMOD_INVALID:
       *message = "CHOLMOD failure: Invalid input.";